First, I've modified the ebuild so I can compile in ~amd64 by changing:

->=media-sound/wavplay-1.4
+wavplay? ( >=media-sound/wavplay-1.4 )

But whenever I try to compile gimp-gap I get this error:

/usr/lib/gcc/x86_64-pc-linux-gnu/4.1.1/../../../../x86_64-pc-linux-gnu/bin/ld: bitstream.o: no se puede usar la reubicación R_X86_64_32 contra `a local symbol' cuando se hace un objeto compartido; recompile con -fPIC
bitstream.o: no se puede leer símbolos: Valor erróneo
collect2: ld devolvió el estado de salida 1
make[4]: *** [libavcodec.so] Error 1
make[4]: se sale del directorio `/var/tmp/portage/gimp-gap-2.2.1/work/gimp-gap-2.2.1/extern_libs/ffmpeg/libavcodec'
make[3]: *** [lib] Error 2
make[3]: se sale del directorio `/var/tmp/portage/gimp-gap-2.2.1/work/gimp-gap-2.2.1/extern_libs/ffmpeg'
make[2]: *** [/var/tmp/portage/gimp-gap-2.2.1/work/gimp-gap-2.2.1/extern_libs/ffmpeg/libavformat/libavformat.a] Error 2
make[2]: *** Se espera a que terminen otras tareas....
rm -f libavcodec.a
ar rc libavcodec.a bitstream.o utils.o mem.o allcodecs.o mpegvideo.o jrevdct.o jfdctfst.o jfdctint.o mpegaudio.o ac3enc.o mjpeg.o resample.o resample2.o dsputil.o motion_est.o imgconvert.o imgresample.o mpeg12.o mpegaudiodec.o pcm.o simple_idct.o ratecontrol.o adpcm.o eval.o dv.o error_resilience.o fft.o mdct.o mace.o huffyuv.o cyuv.o raw.o h264.o golomb.o vp3.o asv1.o 4xm.o cabac.o ffv1.o ra144.o ra288.o vcr1.o cljr.o roqvideo.o dpcm.o interplayvideo.o xan.o rpza.o cinepak.o msrle.o msvideo1.o vqavideo.o idcinvideo.o adx.o rational.o faandct.o 8bps.o smc.o parser.o flicvideo.o truemotion1.o vmdav.o lcl.o qtrle.o g726.o flac.o vp3dsp.o integer.o snow.o tscc.o sonic.o ulti.o h264idct.o qdrw.o xl.o rangecoder.o png.o pnm.o qpeg.o vc9.o h263.o h261.o msmpeg4.o h263dec.o svq1.o rv10.o wmadec.o indeo3.o shorten.o loco.o alac.o wnv1.o ws-snd1.o aasc.o  a52dec.o liba52/bit_allocate.o liba52/bitstream.o liba52/downmix.o liba52/imdct.o  liba52/parse.o liba52/crc.o liba52/resample.o
ranlib libavcodec.a
x86_64-pc-linux-gnu-gcc -shared -o libavcodec.so bitstream.o utils.o mem.o allcodecs.o mpegvideo.o jrevdct.o jfdctfst.o jfdctint.o mpegaudio.o ac3enc.o mjpeg.o resample.o resample2.o dsputil.o motion_est.o imgconvert.o imgresample.o mpeg12.o mpegaudiodec.o pcm.o simple_idct.o ratecontrol.o adpcm.o eval.o dv.o error_resilience.o fft.o mdct.o mace.o huffyuv.o cyuv.o raw.o h264.o golomb.o vp3.o asv1.o 4xm.o cabac.o ffv1.o ra144.o ra288.o vcr1.o cljr.o roqvideo.o dpcm.o interplayvideo.o xan.o rpza.o cinepak.o msrle.o msvideo1.o vqavideo.o idcinvideo.o adx.o rational.o faandct.o 8bps.o smc.o parser.o flicvideo.o truemotion1.o vmdav.o lcl.o qtrle.o g726.o flac.o vp3dsp.o integer.o snow.o tscc.o sonic.o ulti.o h264idct.o qdrw.o xl.o rangecoder.o png.o pnm.o qpeg.o vc9.o h263.o h261.o msmpeg4.o h263dec.o svq1.o rv10.o wmadec.o indeo3.o shorten.o loco.o alac.o wnv1.o ws-snd1.o aasc.o  a52dec.o liba52/bit_allocate.o liba52/bitstream.o liba52/downmix.o liba52/imdct.o  liba52/parse.o liba52/crc.o liba52/resample.o  -lm -lz -ldl  -Wl,--warn-common -rdynamic
/usr/lib/gcc/x86_64-pc-linux-gnu/4.1.1/../../../../x86_64-pc-linux-gnu/bin/ld: bitstream.o: no se puede usar la reubicación R_X86_64_32 contra `a local symbol' cuando se hace un objeto compartido; recompile con -fPIC
bitstream.o: no se puede leer símbolos: Valor erróneo
collect2: ld devolvió el estado de salida 1
make[4]: *** [libavcodec.so] Error 1
make[4]: se sale del directorio `/var/tmp/portage/gimp-gap-2.2.1/work/gimp-gap-2.2.1/extern_libs/ffmpeg/libavcodec'
make[3]: *** [lib] Error 2
make[3]: se sale del directorio `/var/tmp/portage/gimp-gap-2.2.1/work/gimp-gap-2.2.1/extern_libs/ffmpeg'
make[2]: *** [/var/tmp/portage/gimp-gap-2.2.1/work/gimp-gap-2.2.1/extern_libs/ffmpeg/libavcodec/libavcodec.a] Error 2
make[2]: se sale del directorio `/var/tmp/portage/gimp-gap-2.2.1/work/gimp-gap-2.2.1/extern_libs'
make[1]: *** [all-recursive] Error 1
make[1]: se sale del directorio `/var/tmp/portage/gimp-gap-2.2.1/work/gimp-gap-2.2.1'
make: *** [all] Error 2

!!! ERROR: media-plugins/gimp-gap-2.2.1 failed.
Call stack:
  ebuild.sh, line 1546:   Called dyn_compile
  ebuild.sh, line 937:   Called src_compile
  gimp-gap-2.2.1.ebuild, line 28:   Called die

!!! emake failed
!!! If you need support, post the topmost build error, and the call stack if relevant.

!!! This ebuild is from an overlay: '/usr/local/portage'

Here is my emerge --info

Portage 2.1.1-r1 (default-linux/amd64/2006.1/desktop, gcc-4.1.1, glibc-2.4-r3, 2.6.17-gentoo-r7 x86_64)
=================================================================
System uname: 2.6.17-gentoo-r7 x86_64 AMD Athlon(tm) 64 X2 Dual Core Processor 3800+
Gentoo Base System version 1.12.5
Last Sync: Sun, 15 Oct 2006 01:53:01 +0000
app-admin/eselect-compiler: [Not Present]
dev-java/java-config: 1.3.7, 2.0.30
dev-lang/python:     2.4.3-r4
dev-python/pycrypto: 2.0.1-r5
dev-util/ccache:     [Not Present]
dev-util/confcache:  [Not Present]
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-r3
sys-devel/gcc-config: 1.3.13-r4
sys-devel/libtool:   1.5.22
virtual/os-headers:  2.6.11-r2
ACCEPT_KEYWORDS="amd64"
AUTOCLEAN="yes"
CBUILD="x86_64-pc-linux-gnu"
CFLAGS="-march=athlon64 -O2 -pipe -msse3"
CHOST="x86_64-pc-linux-gnu"
CONFIG_PROTECT="/etc /usr/kde/3.5/env /usr/kde/3.5/share/config /usr/kde/3.5/shutdown /usr/share/X11/xkb /usr/share/config /usr/share/texmf/dvipdfm/config/ /usr/share/texmf/dvips/config/ /usr/share/texmf/tex/generic/config/ /usr/share/texmf/tex/platex/config/ /usr/share/texmf/xdvi/"
CONFIG_PROTECT_MASK="/etc/env.d /etc/env.d/java/ /etc/gconf /etc/java-config/vms/ /etc/revdep-rebuild /etc/terminfo"
CXXFLAGS="-march=athlon64 -O2 -pipe -msse3"
DISTDIR="/usr/portage/distfiles"
FEATURES="autoconfig distlocks metadata-transfer prelink sfperms strict"
GENTOO_MIRRORS="ftp://gentoo.mirrors.tds.net/gentoo/ http://ftp.belnet.be/mirror/rsync.gentoo.org/gentoo/ ftp://ftp.belnet.be/mirror/rsync.gentoo.org/gentoo/"
LANG="es_ES.UTF-8"
LDFLAGS="-Wl,-O1"
LINGUAS="es en es_AR es_ES en_GB en_US"
MAKEOPTS="-j3"
PKGDIR="/usr/portage/packages"
PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times --compress --force --whole-file --delete --delete-after --stats --timeout=180 --exclude='/distfiles' --exclude='/local' --exclude='/packages'"
PORTAGE_TMPDIR="/var/tmp"
PORTDIR="/usr/portage"
PORTDIR_OVERLAY="/usr/local/portage /usr/portage/local/layman/zugaina"
SYNC="rsync://rsync.europe.gentoo.org/gentoo-portage"
USE="amd64 X a52 aac acpi alsa apache2 apm arts audiofile avi bash-completion bcmath berkdb bitmap-fonts bzip2 cairo cdr cjk cli crypt cups curl dbus dbx dga dio dlloader doc dri dvd dvdr dvdread eds elibc_glibc emacs emboss encode esd ethereal fam fbcon ffmpeg firefox flac foomaticdb fortran ftp gd gdbm gif gimpprint glut glx gmp gnome gpm gstreamer gtk gtk2 gtkhtml hal ieee1394 imagemagick input_devices_evdev input_devices_keyboard input_devices_mouse ionotify ipv6 isdnlog jabber java jpeg kernel_linux ldap libg++ libwww linguas_en linguas_en_GB linguas_en_US linguas_es linguas_es_AR linguas_es_ES lm_sensors mad mikmod mmx2 mp3 mpeg mysql mysqli ncurses nls nptl nptlonly nvidia ogg opengl pam pcre pdflib perl php png posix postgres ppds pppd python qt3 qt4 quicktime readline reflection samba sdl session speex spell spl ssl svg tcltk tcpd tetex threads tidy tiff truetype truetype-fonts type1-fonts udev unicode usb userland_GNU userlocales v4l vhosts video_cards_nv video_cards_nvidia video_cards_v4l video_cards_vesa video_cards_vga vorbis xinerama xml xorg xv xvid zlib"
Unset:  CTARGET, EMERGE_DEFAULT_OPTS, INSTALL_MASK, LC_ALL, PORTAGE_RSYNC_EXTRA_OPTS