When trying to port dev-util/callgrind to the newest version, I had problems with linking against the valgrind libraries. Quick look into /usr/lib/pkgconfig/valgrind.pc gave this: Libs: -L${libdir}/valgrind/@VG_PLATFORM@ -lcoregrind -lvex -lgcc Notice the @VG_PLATFORM@. As a different note, valgrind-3.2.1 is out too ;)
After bumping the version to 3.2.1, valgrind built fine and even works, but the @VG_PLATFORM@ problem is still there. :(
I checked in 3.2.1 and this problem should be fixed in that ebuild. Thanks for the report.