[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/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 89ba7e6..3b72f0f 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -6037,8 +6037,8 @@
 
 public:
   OMPClauseWriter(ASTRecordWriter &Record) : Record(Record) {}
-#define OPENMP_CLAUSE(Name, Class) void Visit##Class(Class *S);
-#include "clang/Basic/OpenMPKinds.def"
+#define OMP_CLAUSE_CLASS(Enum, Str, Class) void Visit##Class(Class *S);
+#include "llvm/Frontend/OpenMP/OMPKinds.def"
   void writeClause(OMPClause *C);
   void VisitOMPClauseWithPreInit(OMPClauseWithPreInit *C);
   void VisitOMPClauseWithPostUpdate(OMPClauseWithPostUpdate *C);
@@ -6051,7 +6051,7 @@
 }
 
 void OMPClauseWriter::writeClause(OMPClause *C) {
-  Record.push_back(C->getClauseKind());
+  Record.push_back(unsigned(C->getClauseKind()));
   Visit(C);
   Record.AddSourceLocation(C->getBeginLoc());
   Record.AddSourceLocation(C->getEndLoc());