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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210197 91177308-0d34-0410-b5e6-96231b3b80d8
MS-ABI: Mangle empty template parameter packs correctly

Tested for compatibility with VS2013.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210198 91177308-0d34-0410-b5e6-96231b3b80d8