[OpenMP] Silence build warnings when built with MinGW

There's an attempt to upstream this change in
https://github.com/intel/ittapi/pull/25 too.

Differential Revision: https://reviews.llvm.org/D114069

GitOrigin-RevId: 9b2b54983765abd365f6e43428c6a2697c8e4c03
1 file changed