Add popcnt feature flag to match gcc. This flag is implied when sse42 is enabled, but can be disabled separately. Move popcnt intrinsics to popcntintrin.h to match gcc.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@147340 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed