Disable warning C4267 for MSVC. Otherwise it generate literally thousands of...

Disable warning C4267 for MSVC. Otherwise it generate literally thousands of warnings when targeting x64. The warning occurs because int is 32 bit but size_t is 64 bit on Win64.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@116274 91177308-0d34-0410-b5e6-96231b3b80d8