[OPENMP50]Add support for extended device clause in target directives.

Added parsing/sema/serialization support for extended device clause in
executable target directives.
diff --git a/clang/lib/AST/OpenMPClause.cpp b/clang/lib/AST/OpenMPClause.cpp
index b01aae4..a957890 100644
--- a/clang/lib/AST/OpenMPClause.cpp
+++ b/clang/lib/AST/OpenMPClause.cpp
@@ -1433,6 +1433,11 @@
 
 void OMPClausePrinter::VisitOMPDeviceClause(OMPDeviceClause *Node) {
   OS << "device(";
+  OpenMPDeviceClauseModifier Modifier = Node->getModifier();
+  if (Modifier != OMPC_DEVICE_unknown) {
+    OS << getOpenMPSimpleClauseTypeName(Node->getClauseKind(), Modifier)
+       << ": ";
+  }
   Node->getDevice()->printPretty(OS, nullptr, Policy, 0);
   OS << ")";
 }