[clang][OpenMP] OMPFlushClause is synthetic, no such clause exists


[clang][OpenMP] OMPFlushClause is synthetic, no such clause exists

As discussed in https://reviews.llvm.org/D57112#inline-506781,
'flush' clause does not exist in the OpenMP spec, it can not be
specified, and OMPFlushClause class is just a helper class.

Therefore OPENMP_CLAUSE() in clang/Basic/OpenMPKinds.def
should not contain 'flush' "clause".

I have simply removed the OPENMP_CLAUSE(flush, OMPFlushClause)
from clang/Basic/OpenMPKinds.def, grepped for OPENMP_CLAUSE
and added OPENMP_CLAUSE(flush, OMPFlushClause) back to the every
place where OPENMP_CLAUSE is defined and clang/Basic/OpenMPKinds.def
is then included.

So as-is, this patch is a NFC. Possibly, some of these
OPENMP_CLAUSE(flush, OMPFlushClause) should be dropped,
i don't really know.

Test plan: ninja check-clang

Reviewers: ABataev

Reviewed By: ABataev

Subscribers: guansong, arphaman, cfe-commits

Tags: #openmp

Differential Revision: https://reviews.llvm.org/D57280