This matches the Intel documentation which shows them available by importing immintrin.h. x86intrin.h also includes immintrin.h so anyone including x86intrin.h will still get them.
This is different than gcc, but I don't think we were a perfect match there already. I'm unclear what gcc's policy is about how they choose which to add things to.
Differential Revision: https://reviews.llvm.org/D47182
llvm-svn: 333110