MS-ABI: Implement user defined literals

Straightforward implementation of UDLs, it's compatible with VS "14".

This nearly completes our implementation of C++ name mangling for the
MS-ABI.

llvm-svn: 210197
diff --git a/clang/test/CodeGenCXX/mangle-ms-cxx11.cpp b/clang/test/CodeGenCXX/mangle-ms-cxx11.cpp
index c174e48..0cd23f51 100644
--- a/clang/test/CodeGenCXX/mangle-ms-cxx11.cpp
+++ b/clang/test/CodeGenCXX/mangle-ms-cxx11.cpp
@@ -130,3 +130,6 @@
 void A::foo() __restrict && {}
 // CHECK-DAG: @"\01?foo@A@PR19361@@QIHAEXXZ"
 }
+
+int operator"" _deg(long double) { return 0; }
+// CHECK-DAG: @"\01??__K_deg@@YAHO@Z"