[OpenMP] Fix issue with directives used in a macro.

Summary:
If directives are used in a macro, clang complains with:
```
src/projects/openmp/runtime/src/kmp_runtime.c:7486:2: error: embedding a directive within macro arguments has undefined behavior [-Werror,-Wembedded-directive]
#if KMP_USE_MONITOR
```

This patch fixes two occurrences of the issue in `kmp_runtime.cpp`.

Reviewers: tlwilmar, jlpeyton, AndreyChurbanov, Hahnfeld

Subscribers: Hahnfeld, openmp-commits

Differential Revision: https://reviews.llvm.org/D25823

llvm-svn: 284728