[OPENMP50]Add support for 'release' clause.

Added full support for 'release' clause in flush|atomic directives.
diff --git a/clang/lib/AST/OpenMPClause.cpp b/clang/lib/AST/OpenMPClause.cpp
index b9156e89..2947665 100644
--- a/clang/lib/AST/OpenMPClause.cpp
+++ b/clang/lib/AST/OpenMPClause.cpp
@@ -118,6 +118,7 @@
   case OMPC_seq_cst:
   case OMPC_acq_rel:
   case OMPC_acquire:
+  case OMPC_release:
   case OMPC_depend:
   case OMPC_threads:
   case OMPC_simd:
@@ -194,6 +195,7 @@
   case OMPC_seq_cst:
   case OMPC_acq_rel:
   case OMPC_acquire:
+  case OMPC_release:
   case OMPC_depend:
   case OMPC_device:
   case OMPC_threads:
@@ -1346,6 +1348,10 @@
   OS << "acquire";
 }
 
+void OMPClausePrinter::VisitOMPReleaseClause(OMPReleaseClause *) {
+  OS << "release";
+}
+
 void OMPClausePrinter::VisitOMPThreadsClause(OMPThreadsClause *) {
   OS << "threads";
 }