I have to rebuild moc to fix linkage. The build fails every time,
independent of CFLAGS and USE flags:

btool: compile:  i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I../.. -I../.. -pthread -O2 -mcpu=athlon-xp -pipe -fomit-frame-pointer -fno-strict-aliasing -Wall -W -I/usr/include/alsa -MT libmp3_decoder_la-mp3.lo -MD -MP -MF .deps/libmp3_decoder_la-mp3.Tpo -c mp3.c  -fPIC -DPIC -o .libs/libmp3_decoder_la-mp3.o
`-mcpu=' is deprecated. Use `-mtune=' or '-march=' instead.
libtool: compile:  i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I../.. -I../.. -pthread -O2 -mcpu=athlon-xp -pipe -fomit-frame-pointer -fno-strict-aliasing -Wall -W -I/usr/include/alsa -MT libmp3_decoder_la-xing.lo -MD -MP -MF .deps/libmp3_decoder_la-xing.Tpo -c xing.c  -fPIC -DPIC -o .libs/libmp3_decoder_la-xing.o
`-mcpu=' is deprecated. Use `-mtune=' or '-march=' instead.
mv -f .deps/libmp3_decoder_la-xing.Tpo .deps/libmp3_decoder_la-xing.Plo
mv -f .deps/libmp3_decoder_la-mp3.Tpo .deps/libmp3_decoder_la-mp3.Plo
/bin/bash ../../libtool --tag=CC   --mode=link i686-pc-linux-gnu-gcc -I../.. -pthread -O2 -mcpu=athlon-xp -pipe -fomit-frame-pointer -fno-strict-aliasing -Wall -W -I/usr/include/alsa    -module -avoid-version -Wl,-O1 -Wl,--sort-common -Wl,--as-needed -s -export-dynamic -o libmp3_decoder.la -rpath /usr/lib/moc/decoder_plugins libmp3_decoder_la-mp3.lo libmp3_decoder_la-xing.lo -lmad -lid3tag -lz  -lm -ldl
libtool: link: i686-pc-linux-gnu-gcc -shared  .libs/libmp3_decoder_la-mp3.o .libs/libmp3_decoder_la-xing.o   -lmad /usr/lib/libid3tag.so /usr/local/bin/usr/bin/bin/opt/bin/usr/i686-pc-linux-gnu/gcc-bin/4.3.1/opt/intel/cc/10.1.017/bin/usr/lib/plan9/bin/usr/kde/4.1/bin/usr/kde/3.5/bin/usr/qt/3/bin/usr/games/bin/opt/openoffice.org3/program/ -lz -lm -ldl  -pthread -mcpu=athlon-xp -Wl,-O1 -Wl,--sort-common -Wl,--as-needed   -pthread -Wl,-soname -Wl,libmp3_decoder.so -o .libs/libmp3_decoder.so
i686-pc-linux-gnu-gcc: /usr/local/bin/usr/bin/bin/opt/bin/usr/i686-pc-linux-gnu/gcc-bin/4.3.1/opt/intel/cc/10.1.017/bin/usr/lib/plan9/bin/usr/kde/4.1/bin/usr/kde/3.5/bin/usr/qt/3/bin/usr/games/bin/opt/openoffice.org3/program/: No such file or directory
make[3]: *** [libmp3_decoder.la] Error 1
make[3]: Leaving directory `/var/tmp/portage/media-sound/moc-2.5.0_alpha3-r2/work/moc-2.5.0-alpha3/decoder_plugins/mp3'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/var/tmp/portage/media-sound/moc-2.5.0_alpha3-r2/work/moc-2.5.0-alpha3/decoder_plugins'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/var/tmp/portage/media-sound/moc-2.5.0_alpha3-r2/work/moc-2.5.0-alpha3'
make: *** [all] Error 2

That happens both with Paludis and Portage. Does anyone have an idea what goes wrong?