[flang][OpenMP] 'no_openmp_constructs' added to clang broke flang build (llvm#126145)

Adding 'no_openmp_constructs' assumption clause to clang broke the flang
build. Adding to flang so it builds.

Testing
- Build
- Testing: check-all

Author: ddpagan

flang/lib/Lower/OpenMP/Clauses.cpp

@@ -202,6 +202,7 @@ MAKE_EMPTY_CLASS(Mergeable, Mergeable);
 MAKE_EMPTY_CLASS(Nogroup, Nogroup);
 MAKE_EMPTY_CLASS(NoOpenmp, NoOpenmp);
 MAKE_EMPTY_CLASS(NoOpenmpRoutines, NoOpenmpRoutines);
+MAKE_EMPTY_CLASS(NoOpenmpConstructs, NoOpenmpConstructs);
 MAKE_EMPTY_CLASS(NoParallelism, NoParallelism);
 MAKE_EMPTY_CLASS(Notinbranch, Notinbranch);
 MAKE_EMPTY_CLASS(Nowait, Nowait);
@@ -1035,6 +1036,7 @@ Nontemporal make(const parser::OmpClause::Nontemporal &inp,
 
 // NoOpenmp: empty
 // NoOpenmpRoutines: empty
+// NoOpenmpConstructs: empty
 // NoParallelism: empty
 // Notinbranch: empty
 

flang/lib/Lower/OpenMP/Clauses.h

@@ -242,6 +242,8 @@ using Mergeable = tomp::clause::MergeableT<TypeTy, IdTy, ExprTy>;
 using Message = tomp::clause::MessageT<TypeTy, IdTy, ExprTy>;
 using NoOpenmp = tomp::clause::NoOpenmpT<TypeTy, IdTy, ExprTy>;
 using NoOpenmpRoutines = tomp::clause::NoOpenmpRoutinesT<TypeTy, IdTy, ExprTy>;
+using NoOpenmpConstructs =
+    tomp::clause::NoOpenmpConstructsT<TypeTy, IdTy, ExprTy>;
 using NoParallelism = tomp::clause::NoParallelismT<TypeTy, IdTy, ExprTy>;
 using Nocontext = tomp::clause::NocontextT<TypeTy, IdTy, ExprTy>;
 using Nogroup = tomp::clause::NogroupT<TypeTy, IdTy, ExprTy>;

flang/lib/Semantics/check-omp-structure.cpp

@@ -2966,6 +2966,7 @@ CHECK_SIMPLE_CLAUSE(Indirect, OMPC_indirect)
 CHECK_SIMPLE_CLAUSE(Mergeable, OMPC_mergeable)
 CHECK_SIMPLE_CLAUSE(NoOpenmp, OMPC_no_openmp)
 CHECK_SIMPLE_CLAUSE(NoOpenmpRoutines, OMPC_no_openmp_routines)
+CHECK_SIMPLE_CLAUSE(NoOpenmpConstructs, OMPC_no_openmp_constructs)
 CHECK_SIMPLE_CLAUSE(NoParallelism, OMPC_no_parallelism)
 CHECK_SIMPLE_CLAUSE(Nogroup, OMPC_nogroup)
 CHECK_SIMPLE_CLAUSE(Notinbranch, OMPC_notinbranch)

llvm/include/llvm/Frontend/OpenMP/ClauseT.h

@@ -846,6 +846,12 @@ struct NoOpenmpRoutinesT {
   using EmptyTrait = std::true_type;
 };
 
+// V6.0: [10.6.1] `assumption` clauses
+template <typename T, typename I, typename E> //
+struct NoOpenmpConstructsT {
+  using EmptyTrait = std::true_type;
+};
+
 // V5.2: [8.3.1] `assumption` clauses
 template <typename T, typename I, typename E> //
 struct NoParallelismT {
@@ -1239,7 +1245,7 @@ using EmptyClausesT = std::variant<
     ReverseOffloadT<T, I, E>, SeqCstT<T, I, E>, SimdT<T, I, E>,
     ThreadsT<T, I, E>, UnifiedAddressT<T, I, E>, UnifiedSharedMemoryT<T, I, E>,
     UnknownT<T, I, E>, UntiedT<T, I, E>, UseT<T, I, E>, WeakT<T, I, E>,
-    WriteT<T, I, E>>;
+    WriteT<T, I, E>, NoOpenmpConstructsT<T, I, E>>;
 
 template <typename T, typename I, typename E>
 using IncompleteClausesT =