This uses the same logic as in c2b256a990590dc8b69930259650cfeb085add03;
we can't check defined(_MSC_VER) invoked as %clang_cc1, therefore
check for !defined(__MINGW32__) instead.
This fixes the same issue in a new testcase that was added after this
issue was fixed last time in c2b256a990590dc8b69930259650cfeb085add03.
Differential Revision: https://reviews.llvm.org/D151661