[OpenMP] Parsing and sema support for target update directive

Summary:
This patch is to add parsing and sema support for `target update` directive. Support for the `to` and `from` clauses will be added by a different patch.  This patch also adds support for other clauses that are already implemented upstream and apply to `target update`, e.g. `device` and `if`.

This patch is based on the original post by Kelvin Li.

Reviewers: hfinkel, carlo.bertolli, kkwli0, arpith-jacob, ABataev

Subscribers: caomhin, cfe-commits

Differential Revision: http://reviews.llvm.org/D15944

llvm-svn: 270878
diff --git a/clang/lib/AST/StmtProfile.cpp b/clang/lib/AST/StmtProfile.cpp
index 30e094c..3f0391e 100644
--- a/clang/lib/AST/StmtProfile.cpp
+++ b/clang/lib/AST/StmtProfile.cpp
@@ -656,6 +656,11 @@
 
 void OMPClauseProfiler::VisitOMPDefaultmapClause(const OMPDefaultmapClause *) {}
 
+void StmtProfiler::VisitOMPTargetUpdateDirective(
+    const OMPTargetUpdateDirective *S) {
+  VisitOMPExecutableDirective(S);
+}
+
 void StmtProfiler::VisitExpr(const Expr *S) {
   VisitStmt(S);
 }