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

This reverts commit c18d55998b3352e6ec92ccb8a3240a16a57c61e6.

Bots have reported uses that need changing, e.g.,
  clang-tools-extra/clang-tidy/openmp/UseDefaultNoneCheck.cp
as reported by
  http://lab.llvm.org:8011/builders/clang-ppc64be-linux/builds/46591
diff --git a/clang/lib/AST/OpenMPClause.cpp b/clang/lib/AST/OpenMPClause.cpp
index 1cd178c..4b7ebbb 100644
--- a/clang/lib/AST/OpenMPClause.cpp
+++ b/clang/lib/AST/OpenMPClause.cpp
@@ -31,20 +31,20 @@
   switch (getClauseKind()) {
   default:
     break;
-#define OMP_CLAUSE_CLASS(Enum, Str, Class)                                           \
-  case Enum:                                                                   \
+#define OPENMP_CLAUSE(Name, Class)                                             \
+  case OMPC_##Name:                                                            \
     return static_cast<Class *>(this)->children();
-#include "llvm/Frontend/OpenMP/OMPKinds.def"
+#include "clang/Basic/OpenMPKinds.def"
   }
   llvm_unreachable("unknown OMPClause");
 }
 
 OMPClause::child_range OMPClause::used_children() {
   switch (getClauseKind()) {
-#define OMP_CLAUSE_CLASS(Enum, Str, Class)                                           \
-  case Enum:                                                                   \
+#define OPENMP_CLAUSE(Name, Class)                                             \
+  case OMPC_##Name:                                                            \
     return static_cast<Class *>(this)->used_children();
-#include "llvm/Frontend/OpenMP/OMPKinds.def"
+#include "clang/Basic/OpenMPKinds.def"
   case OMPC_threadprivate:
   case OMPC_uniform:
   case OMPC_device_type: