GCC3 provides include files to be placed in /usr/include on powerpc,
i386, and x86_64 machines to support AltiVec, MMX, and SSE/SSE2.

<altivec.h> from gnu/dist/gcc/gcc/config/rs6000/altivec.h
<mmintrin.h> from gnu/dist/gcc/gcc/config/i386/mmintrin.h
<xmmintrin.h> from gnu/dist/gcc/gcc/config/i386/xmmintrin.h

I've committed a change which causes these to be installed so
that programs can use them.
-- 
Matt Thomas                     email: matt@3am-software.com
3am Software Foundry              www: http://3am-software.com/bio/matt/
Cupertino, CA              disclaimer: I avow all knowledge of this 
message.