[OPENMP50]Support for acquire clause.

Added full support for acquire clause in flush|atomic directives.
diff --git a/clang/lib/AST/OpenMPClause.cpp b/clang/lib/AST/OpenMPClause.cpp
index b1f9ad1..b9156e89 100644
--- a/clang/lib/AST/OpenMPClause.cpp
+++ b/clang/lib/AST/OpenMPClause.cpp
@@ -117,6 +117,7 @@
   case OMPC_capture:
   case OMPC_seq_cst:
   case OMPC_acq_rel:
+  case OMPC_acquire:
   case OMPC_depend:
   case OMPC_threads:
   case OMPC_simd:
@@ -192,6 +193,7 @@
   case OMPC_capture:
   case OMPC_seq_cst:
   case OMPC_acq_rel:
+  case OMPC_acquire:
   case OMPC_depend:
   case OMPC_device:
   case OMPC_threads:
@@ -1340,6 +1342,10 @@
   OS << "acq_rel";
 }
 
+void OMPClausePrinter::VisitOMPAcquireClause(OMPAcquireClause *) {
+  OS << "acquire";
+}
+
 void OMPClausePrinter::VisitOMPThreadsClause(OMPThreadsClause *) {
   OS << "threads";
 }