[X86] Add __popcntd and __popcntq to ia32intrin.h to match gcc and icc. Remove...

[X86] Add __popcntd and __popcntq to ia32intrin.h to match gcc and icc. Remove popcnt feature flag from _popcnt32/_popcnt64 and move to ia32intrin.h to match gcc

gcc and icc both implement popcntd and popcntq which we did not. gcc doesn't seem to require a feature flag for the _popcnt32/_popcnt64 spelling and will use a libcall if its not supported.

Differential Revision: https://reviews.llvm.org/D59567

llvm-svn: 356689