[OpenMP] Initial implementation of parse+sema for clause use_device_ptr of 'target data'

http://reviews.llvm.org/D21904

This patch is similar to the implementation of 'private' clause: it adds a list of private pointers to be used within the target data region to store the device pointers returned by the runtime.
Please refer to the following document for a full description of what the runtime witll return in this case (page 10 and 11):
https://github.com/clang-omp/OffloadingDesign

I am happy to answer any question related to the runtime interface to help reviewing this patch.

llvm-svn: 275271
diff --git a/clang/lib/Serialization/ASTWriterStmt.cpp b/clang/lib/Serialization/ASTWriterStmt.cpp
index 2d3a24d..5322d0d 100644
--- a/clang/lib/Serialization/ASTWriterStmt.cpp
+++ b/clang/lib/Serialization/ASTWriterStmt.cpp
@@ -2140,6 +2140,14 @@
   }
 }
 
+void OMPClauseWriter::VisitOMPUseDevicePtrClause(OMPUseDevicePtrClause *C) {
+  Record.push_back(C->varlist_size());
+  Record.AddSourceLocation(C->getLParenLoc());
+  for (auto *VE : C->varlists()) {
+    Record.AddStmt(VE);
+  }
+}
+
 //===----------------------------------------------------------------------===//
 // OpenMP Directives.
 //===----------------------------------------------------------------------===//