Bugzilla Bug 131390

re2c-0.9.11 compiles without any problems on amd64.

Portage 2.1_pre9-r4 (default-linux/amd64/2006.0, gcc-4.1.0, glibc-2.4-r1,
2.6.16-gentoo x86_64)
=================================================================
System uname: 2.6.16-gentoo x86_64 AMD Athlon(tm) 64 Processor 3200+
Gentoo Base System version 1.12.0_pre18
dev-lang/python:     2.4.2-r1
sys-apps/sandbox:    1.2.17
sys-devel/autoconf:  2.13, 2.59-r7
sys-devel/automake:  1.4_p6, 1.5, 1.6.3, 1.7.9-r1, 1.8.5-r3, 1.9.6-r2
sys-devel/binutils:  2.16.1-r2
sys-devel/libtool:   1.5.22
virtual/os-headers:  2.6.11-r3
ACCEPT_KEYWORDS="amd64 ~amd64"
AUTOCLEAN="yes"
CBUILD="x86_64-pc-linux-gnu"
CFLAGS="-march=k8 -O3 -pipe -floop-optimize2 -fno-omit-frame-pointer"
CHOST="x86_64-pc-linux-gnu"
CONFIG_PROTECT="/etc /usr/kde/2/share/config /usr/kde/3.5/env
/usr/kde/3.5/share/config /usr/kde/3.5/shutdown /usr/kde/3/share/config
/usr/lib64/mozilla/defaults/pref /usr/share/X11/xkb /usr/share/config
/var/qmail/control"
CONFIG_PROTECT_MASK="/etc/eselect/compiler /etc/gconf /etc/revdep-rebuild
/etc/terminfo /etc/texmf/web2c /etc/env.d"
CXXFLAGS="-march=k8 -O3 -pipe -floop-optimize2 -fno-omit-frame-pointer"
DISTDIR="/usr/portage/distfiles"
FEATURES="autoconfig distlocks metadata-transfer sandbox sfperms strict"
GENTOO_MIRRORS="ftp://gentoo.chem.wisc.edu/gentoo/"
LANG="en_US.utf8"
LC_ALL="en_US.utf8"
LINGUAS="en_US"
MAKEOPTS="-j2"
PKGDIR="/usr/portage/packages"
PORTAGE_TMPDIR="/var/tmp"
PORTDIR="/usr/portage"
PORTDIR_OVERLAY="/usr/local/portage"
SYNC="rsync://rsync.us.gentoo.org/gentoo-portage"
USE="amd64 X X509 Xaw3d a52 aac alsa apache2 arts async automount avi
bash-completion bcmath berkdb bitmap-fonts browserplugin bzip2 cairo cdr
clearcase cli crypt cups cvs dbus dga djbfft djvu dlloader doc dri dts dvd
dvdread dvi dxr3 ecc eds emboss encode esd examples exif expat fame ffmpeg
firefox flac fltk foomaticdb fortran gd gdbm ggi gif glitz gmp gnome gnutls
gpgme gpm graphviz gs gstreamer gtk gtk2 hal idea imagemagick imlib isdnlog
java javascript jpeg jpeg2k kde kerberos krb4 lcms lesstif libedit lirc
logrotate lzo lzw lzw-tiff mad mailwrapper md5sum mjpeg mng motif mozdevelop
mozilla mp3 mpeg musepack musicbrainz mysql mysqli nautilus ncurses neXt nfs
nls nntp nptl nsplugin ntpl nvidia ogg openal openexr opengl oss pam pcntl pcre
pdflib perl php physfs png posix ppds pppd pwdb python qt qt4 quicktime
readline reflection rle rtc ruby samba sdk sdl session simplexml smime sndfile
source speex spell spl sql sqlite ssl subversion symlink syslog t1lib tcltk
tcpd tetex theora threads tidy tiff timidity toolbar tools truetype
truetype-fonts type1-fonts unicode urandom usb v4l v4l2 vhosts vorbis
vorbis-psy winbind xcomposite xine xml xml2 xmldoclet xmlreader xmlrpc
xmlwriter xmms xorg xpm xprint xscreensaver xsl xv xvid xvmc zip zlib
elibc_glibc input_devices_keyboard input_devices_mouse kernel_linux
linguas_en_US userland_GNU video_cards_nvidia video_cards_glint
video_cards_v4l"
Unset:  ASFLAGS, CTARGET, EMERGE_DEFAULT_OPTS, INSTALL_MASK, LDFLAGS

not only does it compile, it works, too! Now ~amd64.