[OPENMP50]Add initial support for OpenMP 5.0 iterator.

Added basic parsing/semantic analysis/(de)serialization support for
iterator expression introduced in OpenMP 5.0.
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 8bee34e..1e81e0a 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -1389,6 +1389,7 @@
   if (LangOpts.OpenMP) {
     InitBuiltinType(OMPArraySectionTy, BuiltinType::OMPArraySection);
     InitBuiltinType(OMPArrayShapingTy, BuiltinType::OMPArrayShaping);
+    InitBuiltinType(OMPIteratorTy, BuiltinType::OMPIterator);
   }
 
   // C99 6.2.5p11.