Sema: Predefine size_t in MSVC Compatibility mode

MSVC defines size_t without any explicit declarations.  This change
allows us to be compatible with TUs that depend on this declaration
appearing from nowhere.

llvm-svn: 199190
diff --git a/clang/test/SemaCXX/MicrosoftCompatibility.cpp b/clang/test/SemaCXX/MicrosoftCompatibility.cpp
index a914169..1f27deb 100644
--- a/clang/test/SemaCXX/MicrosoftCompatibility.cpp
+++ b/clang/test/SemaCXX/MicrosoftCompatibility.cpp
@@ -24,6 +24,7 @@
 namespace ms_predefined_types {
   // ::type_info is a built-in forward class declaration.
   void f(const type_info &a);
+  void f(size_t);
 }