[OPENMP] Add support for OMP5 requires directive + unified_address clause

Add support for OMP5.0 requires directive and unified_address clause.
Patches to follow will include support for additional clauses.

Differential Revision: https://reviews.llvm.org/D52359

llvm-svn: 343063
diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
index b706e50..f5de359 100644
--- a/clang/lib/AST/DeclBase.cpp
+++ b/clang/lib/AST/DeclBase.cpp
@@ -810,6 +810,7 @@
     case ObjCCategoryImpl:
     case Import:
     case OMPThreadPrivate:
+    case OMPRequires:
     case OMPCapturedExpr:
     case Empty:
       // Never looked up by name.