[Clang][OpenMP] Return error ahead of time if there are multiple mutex clauses in atomic directive

[tianshilei1992]

Summary

Currently if there are multiple mutex clauses used in atomic directive,
it emits an error but proceeds execution. This patch simply makes it return ahead
of time.

[tianshilei1992]

add another error return for memory order clauses

[tianshilei1992]

ping

[ABataev]

Tests

[tianshilei1992]

Okay, I reached the same point as D115561, that the compiler stops at the first position it encounters error, so all those mixed uses cannot be in the same test case.

[tianshilei1992]

Abandon the change because of the trade off between the amount of changes and benefit.

clang/lib/Sema/SemaOpenMP.cpp

for (const OMPClause *C : Clauses) {
     if (C->getClauseKind() == OMPC_read || C->getClauseKind() == OMPC_write ||
         C->getClauseKind() == OMPC_update ||
         C->getClauseKind() == OMPC_capture) {
       if (AtomicKind != OMPC_unknown) {
         Diag(C->getBeginLoc(), diag::err_omp_atomic_several_clauses)
             << SourceRange(C->getBeginLoc(), C->getEndLoc());
         Diag(AtomicKindLoc, diag::note_omp_previous_mem_order_clause)
             << getOpenMPClauseName(AtomicKind);
+        return StmtError();
       } else {
         AtomicKind = C->getClauseKind();
         AtomicKindLoc = C->getBeginLoc();
       }
     }
     if (C->getClauseKind() == OMPC_seq_cst ||
         C->getClauseKind() == OMPC_acq_rel ||
         C->getClauseKind() == OMPC_acquire ||
         C->getClauseKind() == OMPC_release ||
         C->getClauseKind() == OMPC_relaxed) {
       if (MemOrderKind != OMPC_unknown) {
         Diag(C->getBeginLoc(), diag::err_omp_several_mem_order_clauses)
             << getOpenMPDirectiveName(OMPD_atomic) << 0
             << SourceRange(C->getBeginLoc(), C->getEndLoc());
         Diag(MemOrderLoc, diag::note_omp_previous_mem_order_clause)
             << getOpenMPClauseName(MemOrderKind);
+        return StmtError();
       } else {
         MemOrderKind = C->getClauseKind();
         MemOrderLoc = C->getBeginLoc();
       }
     }
   }
   // OpenMP 5.0, 2.17.7 atomic Construct, Restrictions
   // If atomic-clause is read then memory-order-clause must not be acq_rel or