If isKnownWindowsMSVCEnvironment then getOS == Triple::Win32 and
Environment == Triple::MSVC so it will never be MinGW or Cygwin.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205349 91177308-0d34-0410-b5e6-96231b3b80d8