See summary. This is what I get:

# emerge -1v ant-owanttask
>>> Emerging (1 of 1) dev-java/ant-owanttask-1.1-r12
* owanttask-1.1-gentoo.tar.bz2 SHA256 SHA512 WHIRLPOOL size ;-) ...                                                         [ ok ]
 * Using: icedtea-7
>>> Unpacking source...
>>> Unpacking owanttask-1.1-gentoo.tar.bz2 to /var/tmp/portage/dev-java/ant-owanttask-1.1-r12/work
 * Applying ant-owanttask-1.1-classpath.patch ...                                                                            [ ok ]
>>> Source unpacked in /var/tmp/portage/dev-java/ant-owanttask-1.1-r12/work
>>> Compiling source in /var/tmp/portage/dev-java/ant-owanttask-1.1-r12/work/owanttask-1.1 ...
Rewriting attributes
Rewriting ./build.xml
 * Disabling all optional ANT_TASKS
Buildfile: /var/tmp/portage/dev-java/ant-owanttask-1.1-r12/work/owanttask-1.1/build.xml

compile:
    [mkdir] Created dir: /var/tmp/portage/dev-java/ant-owanttask-1.1-r12/work/owanttask-1.1/output/build
    [javac] Compiling 8 source files to /var/tmp/portage/dev-java/ant-owanttask-1.1-r12/work/owanttask-1.1/output/build
    [javac] An exception has occurred in the compiler (1.7.0_40). Please file a bug at the Java Developer Connection (http://java.sun.com/webapps/bugreport)  after checking the Bug Parade for duplicates. Include your program and the following diagnostic in your report.  Thank you.
    [javac] java.lang.AssertionError
    [javac]     at com.sun.tools.javac.util.Assert.error(Assert.java:126)
    [javac]     at com.sun.tools.javac.util.Assert.check(Assert.java:45)
    [javac]     at com.sun.tools.javac.comp.Attr.attribIdentAsEnumType(Attr.java:678)
    [javac]     at com.sun.tools.javac.comp.MemberEnter.visitVarDef(MemberEnter.java:629)
    [javac]     at com.sun.tools.javac.tree.JCTree$JCVariableDecl.accept(JCTree.java:725)
    [javac]     at com.sun.tools.javac.comp.MemberEnter.memberEnter(MemberEnter.java:401)
    [javac]     at com.sun.tools.javac.comp.Attr.visitVarDef(Attr.java:855)
    [javac]     at com.sun.tools.javac.tree.JCTree$JCVariableDecl.accept(JCTree.java:725)
    [javac]     at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431)
    [javac]     at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:418)
    [javac]     at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:480)
    [javac]     at com.sun.tools.javac.comp.Attr.attribStats(Attr.java:496)
    [javac]     at com.sun.tools.javac.comp.Attr.visitForLoop(Attr.java:939)
    [javac]     at com.sun.tools.javac.tree.JCTree$JCForLoop.accept(JCTree.java:872)
    [javac]     at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431)
    [javac]     at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:418)
    [javac]     at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:480)
    [javac]     at com.sun.tools.javac.comp.Attr.attribStats(Attr.java:496)
    [javac]     at com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:918)
    [javac]     at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:781)
    [javac]     at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431)
    [javac]     at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:418)
    [javac]     at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:480)
    [javac]     at com.sun.tools.javac.comp.Attr.visitTry(Attr.java:1118)
    [javac]     at com.sun.tools.javac.tree.JCTree$JCTry.accept(JCTree.java:1044)
    [javac]     at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431)
    [javac]     at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:418)
    [javac]     at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:480)
    [javac]     at com.sun.tools.javac.comp.Attr.attribStats(Attr.java:496)
    [javac]     at com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:918)
    [javac]     at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:781)
    [javac]     at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431)
    [javac]     at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:418)
    [javac]     at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:480)
    [javac]     at com.sun.tools.javac.comp.Attr.visitMethodDef(Attr.java:836)
    [javac]     at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:669)
    [javac]     at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431)
    [javac]     at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:418)
    [javac]     at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:480)
    [javac]     at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:3250)
    [javac]     at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3173)
    [javac]     at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3109)
    [javac]     at com.sun.tools.javac.comp.Attr.attrib(Attr.java:3083)
    [javac]     at com.sun.tools.javac.main.JavaCompiler.attribute(JavaCompiler.java:1184)
    [javac]     at com.sun.tools.javac.main.JavaCompiler.compile2(JavaCompiler.java:870)
    [javac]     at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:829)
    [javac]     at com.sun.tools.javac.main.Main.compile(Main.java:439)
    [javac]     at com.sun.tools.javac.main.Main.compile(Main.java:353)
    [javac]     at com.sun.tools.javac.main.Main.compile(Main.java:342)
    [javac]     at com.sun.tools.javac.main.Main.compile(Main.java:333)
    [javac]     at com.sun.tools.javac.Main.compile(Main.java:76)
    [javac]     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    [javac]     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    [javac]     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    [javac]     at java.lang.reflect.Method.invoke(Method.java:606)
    [javac]     at org.apache.tools.ant.taskdefs.compilers.Javac13.execute(Javac13.java:56)
    [javac]     at org.apache.tools.ant.taskdefs.Javac.compile(Javac.java:1153)
    [javac]     at org.apache.tools.ant.taskdefs.Javac.execute(Javac.java:930)
    [javac]     at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:291)
    [javac]     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    [javac]     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    [javac]     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    [javac]     at java.lang.reflect.Method.invoke(Method.java:606)
    [javac]     at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
    [javac]     at org.apache.tools.ant.Task.perform(Task.java:348)
    [javac]     at org.apache.tools.ant.Target.execute(Target.java:392)
    [javac]     at org.apache.tools.ant.Target.performTasks(Target.java:413)
    [javac]     at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1399)
    [javac]     at org.apache.tools.ant.Project.executeTarget(Project.java:1368)
    [javac]     at org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExecutor.java:41)
    [javac]     at org.apache.tools.ant.Project.executeTargets(Project.java:1251)
    [javac]     at org.apache.tools.ant.Main.runBuild(Main.java:811)
    [javac]     at org.apache.tools.ant.Main.startAnt(Main.java:217)
    [javac]     at org.apache.tools.ant.launch.Launcher.run(Launcher.java:280)
    [javac]     at org.apache.tools.ant.launch.Launcher.main(Launcher.java:109)

BUILD FAILED
/var/tmp/portage/dev-java/ant-owanttask-1.1-r12/work/owanttask-1.1/build.xml:12: Compile failed; see the compiler error output for details.

Total time: 0 seconds
 * ERROR: dev-java/ant-owanttask-1.1-r12 failed (compile phase):
 *   eant failed
 * 
 * Call stack:
 *     ebuild.sh, line   93:  Called src_compile
 *   environment, line 4145:  Called java-pkg-2_src_compile
 *   environment, line 2108:  Called eant 'jar' '-f' 'build.xml'
 *   environment, line  601:  Called die
 * The specific snippet of code:
 *       ant ${antflags} "${@}" || die "eant failed"
 * 
 * If you need support, post the output of `emerge --info '=dev-java/ant-owanttask-1.1-r12'`,
 * the complete build log and the output of `emerge -pqv '=dev-java/ant-owanttask-1.1-r12'`.
!!! When you file a bug report, please include the following information:
GENTOO_VM=icedtea-7  CLASSPATH="" JAVA_HOME="/usr/lib64/icedtea7"
JAVACFLAGS="-source 1.4 -target 1.4" COMPILER="javac"
and of course, the output of emerge --info =ant-owanttask-1.1

Reproducible: Always

Steps to Reproduce:
1. emerge -1v ant-owanttask
Actual Results:  
Compilation failure.

Expected Results:  
Successful merge.


# emerge --info '=dev-java/ant-owanttask-1.1-r12'
Portage 2.1.12.2 (default/linux/amd64/13.0/desktop/kde, gcc-4.7.3, glibc-2.15-r3, 3.9.11-gentoo-r1 x86_64)
=================================================================
                         System Settings
=================================================================
System uname: Linux-3.9.11-gentoo-r1-x86_64-Intel-R-_Core-TM-_i7-2600_CPU_@_3.40GHz-with-gentoo-2.2
KiB Mem:    16397364 total,    790500 free
KiB Swap:    8171516 total,   8171516 free
Timestamp of tree: Wed, 24 Jul 2013 06:45:01 +0000
ld ld di GNU (GNU Binutils) 2.23.1
distcc 3.1 x86_64-pc-linux-gnu [enabled]
ccache version 3.1.9 [enabled]
app-shells/bash:          4.2_p45
dev-java/java-config:     2.1.12-r1
dev-lang/python:          2.7.5, 3.2.5-r1
dev-util/ccache:          3.1.9
dev-util/cmake:           2.8.10.2-r2
dev-util/pkgconfig:       0.28
sys-apps/baselayout:      2.2
sys-apps/openrc:          0.11.8
sys-apps/sandbox:         2.6-r1
sys-devel/autoconf:       2.13, 2.69
sys-devel/automake:       1.11.6, 1.12.6
sys-devel/binutils:       2.23.1
sys-devel/gcc:            4.7.3
sys-devel/gcc-config:     1.7.3
sys-devel/libtool:        2.4-r1
sys-devel/make:           3.82-r4
sys-kernel/linux-headers: 3.7 (virtual/os-headers)
sys-libs/glibc:           2.15-r3
Repositories: gentoo x-portage
ACCEPT_KEYWORDS="amd64"
ACCEPT_LICENSE="* -@EULA"
CBUILD="x86_64-pc-linux-gnu"
CFLAGS="-march=corei7-avx -O2 -pipe -fomit-frame-pointer -flto=8"
CHOST="x86_64-pc-linux-gnu"
CONFIG_PROTECT="/etc /usr/share/config /usr/share/gnupg/qualified.txt"
CONFIG_PROTECT_MASK="/etc/ca-certificates.conf /etc/env.d /etc/fonts/fonts.conf /etc/gconf /etc/gentoo-release /etc/php/apache2-php5.4/ext-active/ /etc/php/cgi-php5.4/ext-active/ /etc/php/cli-php5.4/ext-active/ /etc/revdep-rebuild /etc/sandbox.d /etc/terminfo"
CXXFLAGS="-march=corei7-avx -O2 -pipe -fomit-frame-pointer -flto=8"
DISTDIR="/usr/portage/distfiles"
EMERGE_DEFAULT_OPTS="--keep-going y --with-bdeps y"
FCFLAGS="-O2 -pipe"
FEATURES="assume-digests binpkg-logs ccache compress-build-logs config-protect-if-modified distcc distlocks ebuild-locks merge-sync news parallel-fetch protect-owned sandbox sfperms split-elog split-log strict test unknown-features-warn unmerge-logs unmerge-orphans userfetch userpriv usersandbox usersync xattr"
FFLAGS="-O2 -pipe"
GENTOO_MIRRORS="http://mirror.netcologne.de/gentoo/ http://tux.rainside.sk/gentoo/ http://gentoo.supp.name/ http://mirror.opteamax.de/gentoo/ http://gentoo.mneisen.org/"
LANG="it_IT.UTF-8"
LDFLAGS="-Wl,-O1 -Wl,--as-needed -flto=8"
MAKEOPTS="-j11"
PKGDIR="/usr/portage/packages"
PORTAGE_CONFIGROOT="/"
PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times --compress --force --whole-file --delete --stats --human-readable --timeout=180 --exclude=/distfiles --exclude=/local --exclude=/packages"
PORTAGE_TMPDIR="/var/tmp"
PORTDIR="/usr/portage"
PORTDIR_OVERLAY="/usr/local/portage"
SYNC="rsync://rsync.europe.gentoo.org/gentoo-portage"
USE="X a52 aac aalib acl acpi adns alsa amd64 ao audiofile bash-completion bluetooth branding bzip2 cairo caps cdda cddb cdparanoia cdr cli consolekit cracklib crypt css cups curl cxx dbus declarative dga djvu dri dts dvd dvdr emboss encode exif expat fam fbcon ffmpeg fftw firefox flac fontconfig foomaticdb fortran ftp gd gdbm geoip ggi gif gimp gmp gnutls gphoto2 gpm graphviz gstreamer gtk handbook iconv icu idn ieee1394 imagemagick imlib ipv6 java jbig jpeg jpeg2k kde kipi lame lcms libcaca libnotify libsamplerate lm_sensors lua lzma lzo mad mmap mmx mng modules mp3 mp4 mpeg mplayer mudflap multilib musicbrainz ncurses nls nptl nsplugin offensive ogg openal openexr opengl openmp pam pango pcre pdf phonon plasma png policykit postscript ppds qt3support qt4 rdesktop readline recode sdl semantic-desktop session smartcard sndfile sockets speex spell sqlite sqlite3 sse sse2 ssl startup-notification subversion svg symlink syslog sysvipc taglib tcpd theora threads tidy tiff truetype udev udisks unicode upower usb vcd vdpau vim-syntax vnc vorbis win32codecs wmf wxwidgets x264 xattr xcb xcomposite xinerama xml xpm xscreensaver xv xvid yahoo zlib" ABI_X86="64 32" ALSA_CARDS="hda-intel virmidi" APACHE2_MODULES="authn_core authz_core socache_shmcb unixd actions alias auth_basic authn_alias authn_anon authn_dbm authn_default authn_file authz_dbm authz_default authz_groupfile authz_host authz_owner authz_user autoindex cache cgi cgid dav dav_fs dav_lock deflate dir disk_cache env expires ext_filter file_cache filter headers include info log_config logio mem_cache mime mime_magic negotiation rewrite setenvif speling status unique_id userdir usertrack vhost_alias" CALLIGRA_FEATURES="kexi words flow plan sheets stage tables krita karbon braindump author" CAMERAS="kodak ptp2" COLLECTD_PLUGINS="df interface irq load memory rrdtool swap syslog" ELIBC="glibc" GPSD_PROTOCOLS="ashtech aivdm earthmate evermore fv18 garmin garmintxt gpsclock itrax mtk3301 nmea ntrip navcom oceanserver oldstyle oncore rtcm104v2 rtcm104v3 sirf superstar2 timing tsip tripmate tnt ubx" GRUB_PLATFORMS="pc" INPUT_DEVICES="evdev" KERNEL="linux" LCD_DEVICES="bayrad cfontz cfontz633 glk hd44780 lb216 lcdm001 mtxorb ncurses text" LIBREOFFICE_EXTENSIONS="presenter-minimizer nlpsolver" LINGUAS="it" OFFICE_IMPLEMENTATION="libreoffice" PHP_TARGETS="php5-4" PYTHON_SINGLE_TARGET="python2_7" PYTHON_TARGETS="python2_7 python3_2" RUBY_TARGETS="ruby19 ruby18" USERLAND="GNU" VIDEO_CARDS="radeon r600" XTABLES_ADDONS="quota2 psd pknock lscan length2 ipv4options ipset ipp2p iface geoip fuzzy condition tee tarpit sysrq steal rawnat logmark ipmark dhcpmac delude chaos account"
Unset:  CPPFLAGS, CTARGET, INSTALL_MASK, LC_ALL, PORTAGE_BUNZIP2_COMMAND, PORTAGE_COMPRESS, PORTAGE_COMPRESS_FLAGS, PORTAGE_RSYNC_EXTRA_OPTS, USE_PYTHON

# emerge -pqv '=dev-java/ant-owanttask-1.1-r12'
[ebuild  N    ] dev-java/ant-owanttask-1.1-r12