Add support for the `-fopenmp-version=60` command line argument. It is
needed for https://github.com/llvm/llvm-project/pull/119891 (`#pragma
omp stripe`) which will be the first OpenMP 6.0 directive implemented.
Add regression tests for Clang in `-fopenmp-version=60` mode.
Error directive is allowed in both declared and executable contexts.
The function ActOnOpenMPAtClause is called in both places during the
parsers.
Adding a param "bool InExContext" to identify context which is used to
emit error massage.
Differential Revision: https://reviews.llvm.org/D137851