[Support] Update MSVC compiler support in Compiler.h.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172644 91177308-0d34-0410-b5e6-96231b3b80d8
[Support] Add MSVC intrinsic for CountPopulation.

Patch by Jakub Staszak.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172645 91177308-0d34-0410-b5e6-96231b3b80d8