Gentoo's Bugzilla –
Attachment 394734 Details for
Bug 536916media-libs/mesa-10.3.7[abi_x86_32] - ../../../../src/gallium/auxiliary/.libs/libgallium.a(tgsi_exec.o): In function `micro_imsb': tgsi_exec.c:(.text+0x1ac3): undefined reference to `__clrsbsi2'