[OpenMP] Parsing and sema support for the to clause

Summary:
The patch contains the parsing and sema support for the `to` clause. 

Patch based on the original post by Kelvin Li.

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

Subscribers: caomhin, cfe-commits

Differential Revision: http://reviews.llvm.org/D18597

llvm-svn: 270880
diff --git a/clang/lib/Basic/OpenMPKinds.cpp b/clang/lib/Basic/OpenMPKinds.cpp
index f066c6f..4a3423b 100644
--- a/clang/lib/Basic/OpenMPKinds.cpp
+++ b/clang/lib/Basic/OpenMPKinds.cpp
@@ -162,6 +162,7 @@
   case OMPC_num_tasks:
   case OMPC_hint:
   case OMPC_uniform:
+  case OMPC_to:
     break;
   }
   llvm_unreachable("Invalid OpenMP simple clause kind");
@@ -297,6 +298,7 @@
   case OMPC_num_tasks:
   case OMPC_hint:
   case OMPC_uniform:
+  case OMPC_to:
     break;
   }
   llvm_unreachable("Invalid OpenMP simple clause kind");