[flang][OpenMP] Allow flush of common block (#139528)
I think this was denied by accident in
https://github.com/llvm/llvm-project/commit/68180d8d16f07db8200dfce7bae26a80c43ebc5e.
Flush of a common block is allowed by the standard on my reading. It is
not allowed by classic-flang but is supported by gfortran and ifx.
This doesn't need any lowering changes. The LLVM translation ignores the
flush argument list because the openmp runtime library doesn't support
flushing specific data.
Depends upon https://github.com/llvm/llvm-project/pull/139522. Ignore
the first commit in this PR.
