[ASan/Win] Use clang rather than clang-cl by default for lit tests. Make Windows-only tests explicitly use clang-cl.

Reviewed at http://reviews.llvm.org/D3893

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@209719 91177308-0d34-0410-b5e6-96231b3b80d8