[OPENMP50]Support 'update' clause for 'depobj' directive.

Added basic support (parsing/sema/serialization) for 'update' clause in
'depobj' directive.
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index bf59bca..bf893c7 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -6141,7 +6141,14 @@
 
 void OMPClauseWriter::VisitOMPWriteClause(OMPWriteClause *) {}
 
-void OMPClauseWriter::VisitOMPUpdateClause(OMPUpdateClause *) {}
+void OMPClauseWriter::VisitOMPUpdateClause(OMPUpdateClause *C) {
+  Record.push_back(C->isExtended() ? 1 : 0);
+  if (C->isExtended()) {
+    Record.AddSourceLocation(C->getLParenLoc());
+    Record.AddSourceLocation(C->getArgumentLoc());
+    Record.writeEnum(C->getDependencyKind());
+  }
+}
 
 void OMPClauseWriter::VisitOMPCaptureClause(OMPCaptureClause *) {}