It doesn't seem to be a problem with the ebuild which compiles fine. The problem might be the directory which apc.so goes into and maybe a wrong link in apc.ini since it is not detected neither by php -m nor by a phpinfo page.
1) Please post your `emerge --info' output in a comment. 2) Please post your `emerge -vpq dev-php/pecl-apc' output in a comment. 3) Please post your `emerge -vpq dev-lang/php' output in a comment.
This is most likely a php.ini configuration problem. Try using an unmodified version shipped with the package.
# emerge --info Portage 2.1.11.31 (hardened/linux/amd64/no-multilib, gcc-4.5.4, glibc-2.15-r3, 3.4.9-gentoo x86_64) ================================================================= System uname: Linux-3.4.9-gentoo-x86_64-AMD_Athlon-tm-_II_X4_620_Processor-with-gentoo-2.1 Timestamp of tree: Tue, 11 Dec 2012 22:30:01 +0000 ld GNU ld (GNU Binutils) 2.22 app-shells/bash: 4.2_p37 dev-lang/python: 2.7.3-r2, 3.2.3 dev-util/pkgconfig: 0.27.1 sys-apps/baselayout: 2.1-r1 sys-apps/openrc: 0.11.8 sys-apps/sandbox: 2.5 sys-devel/autoconf: 2.68 sys-devel/automake: 1.11.6 sys-devel/binutils: 2.22-r1 sys-devel/gcc: 4.5.4 sys-devel/gcc-config: 1.7.3 sys-devel/libtool: 2.4-r1 sys-devel/make: 3.82-r3 sys-kernel/linux-headers: 3.6 (virtual/os-headers) sys-libs/glibc: 2.15-r3 Repositories: gentoo ACCEPT_KEYWORDS="amd64" ACCEPT_LICENSE="* -@EULA" CBUILD="x86_64-pc-linux-gnu" CFLAGS="-O2 -pipe" CHOST="x86_64-pc-linux-gnu" CONFIG_PROTECT="/etc" CONFIG_PROTECT_MASK="/etc/ca-certificates.conf /etc/env.d /etc/gconf /etc/gentoo-release /etc/php/apache2-php5.3/ext-active/ /etc/php/apache2-php5.4/ext-active/ /etc/php/cgi-php5.3/ext-active/ /etc/php/cgi-php5.4/ext-active/ /etc/php/cli-php5.3/ext-active/ /etc/php/cli-php5.4/ext-active/ /etc/revdep-rebuild /etc/sandbox.d /etc/terminfo" CXXFLAGS="-O2 -pipe" DISTDIR="/usr/portage/distfiles" FCFLAGS="-O2 -pipe" FEATURES="assume-digests binpkg-logs config-protect-if-modified distlocks ebuild-locks fixlafiles merge-sync news parallel-fetch protect-owned sandbox sfperms strict unknown-features-warn unmerge-logs unmerge-orphans userfetch" FFLAGS="-O2 -pipe" GENTOO_MIRRORS="http://distfiles.gentoo.org" LDFLAGS="-Wl,-O1 -Wl,--as-needed" 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="" SYNC="rsync://rsync.gentoo.org/gentoo-portage" USE="acl amd64 berkdb bzip2 cli cracklib crypt cups cxx dri gdbm gpm hardened iconv ipv6 justify mmx modules mudflap ncurses nls nptl openmp pam pax_kernel pcre pppd readline session sse sse2 ssl tcpd unicode urandom zlib" ALSA_CARDS="ali5451 als4000 atiixp atiixp-modem bt87x ca0106 cmipci emu10k1x ens1370 ens1371 es1938 es1968 fm801 hda-intel intel8x0 intel8x0m maestro3 trident usb-audio via82xx via82xx-modem ymfpci" ALSA_PCM_PLUGINS="adpcm alaw asym copy dmix dshare dsnoop empty extplug file hooks iec958 ioplug ladspa lfloat linear meter mmap_emul mulaw multi null plug rate route share shm softvol" 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" CAMERAS="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" INPUT_DEVICES="keyboard mouse evdev" KERNEL="linux" LCD_DEVICES="bayrad cfontz cfontz633 glk hd44780 lb216 lcdm001 mtxorb ncurses text" LIBREOFFICE_EXTENSIONS="presenter-console presenter-minimizer" PHP_TARGETS="php5-3" PYTHON_SINGLE_TARGET="python2_7" PYTHON_TARGETS="python2_7 python3_2" RUBY_TARGETS="ruby18 ruby19" USERLAND="GNU" VIDEO_CARDS="fbdev glint intel mach64 mga nouveau nv r128 radeon savage sis tdfx trident vesa via vmware dummy v4l" 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, EMERGE_DEFAULT_OPTS, INSTALL_MASK, LANG, LC_ALL, MAKEOPTS, PORTAGE_BUNZIP2_COMMAND, PORTAGE_COMPRESS, PORTAGE_COMPRESS_FLAGS, PORTAGE_RSYNC_EXTRA_OPTS, USE_PYTHON # emerge -vpq dev-php/pecl-apc [ebuild R ] dev-php/pecl-apc-3.1.9-r2 USE="lock_pthreadmutex -lock_pthreadrw -lock_semaphore -lock_spinlock -mmap" PHP_TARGETS="php5-3" # emerge -vpq dev-lang/php [ebuild R ] dev-lang/php-5.4.6 USE="apache2 berkdb bzip2 cli crypt ctype fileinfo filter gd gdbm hash iconv ipv6 json mysql mysqlnd nls phar posix readline session simplexml ssl tokenizer unicode xml xmlreader zlib -bcmath -calendar -cdb -cgi -cjk -curl -curlwrappers -debug -doc -embed -enchant -exif -firebird -flatfile -fpm (-frontbase) -ftp -gmp -imap -inifile -intl -iodbc -kerberos (-kolab) -ldap -ldap-sasl -libedit -mhash -mssql -mysqli -oci8-instant-client -odbc -pcntl -pdo -pic -postgres -qdbm -recode -sharedmem -snmp -soap -sockets -spell -sqlite3 (-sybase-ct) -sysvipc -threads -tidy -truetype -wddx -xmlrpc -xmlwriter -xpm -xsl -zip"
I am using the php.ini shipped with the package.
I found out the problem. In few words pecl-apc is out of date and it relies on php5.3 thus the library is not found by php5.4.
Sorry, but apc does not support 5.4 yet. You can use xcache instead or wait for a stable release.
