[OpenMP][NFCI] Move OpenMP clause information to `lib/Frontend/OpenMP`

This is a cleanup and normalization patch that also enables reuse with
Flang later on. A follow up will clean up and move the directive ->
clauses mapping.

Reviewed By: fghanim

Differential Revision: https://reviews.llvm.org/D77112
diff --git a/clang/lib/AST/OpenMPClause.cpp b/clang/lib/AST/OpenMPClause.cpp
index a205a1b..0fdbec6 100644
--- a/clang/lib/AST/OpenMPClause.cpp
+++ b/clang/lib/AST/OpenMPClause.cpp
@@ -31,20 +31,20 @@
   switch (getClauseKind()) {
   default:
     break;
-#define OPENMP_CLAUSE(Name, Class)                                             \
-  case OMPC_##Name:                                                            \
+#define OMP_CLAUSE_CLASS(Enum, Str, Class)                                           \
+  case Enum:                                                                   \
     return static_cast<Class *>(this)->children();
-#include "clang/Basic/OpenMPKinds.def"
+#include "llvm/Frontend/OpenMP/OMPKinds.def"
   }
   llvm_unreachable("unknown OMPClause");
 }
 
 OMPClause::child_range OMPClause::used_children() {
   switch (getClauseKind()) {
-#define OPENMP_CLAUSE(Name, Class)                                             \
-  case OMPC_##Name:                                                            \
+#define OMP_CLAUSE_CLASS(Enum, Str, Class)                                           \
+  case Enum:                                                                   \
     return static_cast<Class *>(this)->used_children();
-#include "clang/Basic/OpenMPKinds.def"
+#include "llvm/Frontend/OpenMP/OMPKinds.def"
   case OMPC_threadprivate:
   case OMPC_uniform:
   case OMPC_device_type: