Support clang compiling under	windows-gnu and windows-msvc

Patch by Peiyuan Song <squallatf@gmail.com>

Differential Revision: https://reviews.llvm.org/D53422


git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@348756 91177308-0d34-0410-b5e6-96231b3b80d8
18 files changed