[OPENMP50]Add support for relaxed clause in atomic directive.

Added full support for relaxed clause.
diff --git a/clang/lib/AST/OpenMPClause.cpp b/clang/lib/AST/OpenMPClause.cpp
index 2947665..6eac982 100644
--- a/clang/lib/AST/OpenMPClause.cpp
+++ b/clang/lib/AST/OpenMPClause.cpp
@@ -119,6 +119,7 @@
   case OMPC_acq_rel:
   case OMPC_acquire:
   case OMPC_release:
+  case OMPC_relaxed:
   case OMPC_depend:
   case OMPC_threads:
   case OMPC_simd:
@@ -196,6 +197,7 @@
   case OMPC_acq_rel:
   case OMPC_acquire:
   case OMPC_release:
+  case OMPC_relaxed:
   case OMPC_depend:
   case OMPC_device:
   case OMPC_threads:
@@ -1352,6 +1354,10 @@
   OS << "release";
 }
 
+void OMPClausePrinter::VisitOMPRelaxedClause(OMPRelaxedClause *) {
+  OS << "relaxed";
+}
+
 void OMPClausePrinter::VisitOMPThreadsClause(OMPThreadsClause *) {
   OS << "threads";
 }