Reapply r276069 with workaround for MSVC 2013

llvm-svn: 277286
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 9a1e4f6..42e5b35 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -5381,6 +5381,7 @@
   AddSourceLocation(TemplateParams->getTemplateLoc());
   AddSourceLocation(TemplateParams->getLAngleLoc());
   AddSourceLocation(TemplateParams->getRAngleLoc());
+  // TODO: Concepts
   Record->push_back(TemplateParams->size());
   for (const auto &P : *TemplateParams)
     AddDeclRef(P);