[MS Demangler] Add rudimentary C++11 Support

This patch adds support for demangling r-value references, new
operators such as the ""_foo operator, lambdas, alias types,
nullptr_t, and various other C++11'isms.

There is 1 failing test remaining in this file, which appears to
be related to back-referencing. This type of problem has the
potential to get ugly so I'd rather fix it in a separate patch.

Differential Revision: https://reviews.llvm.org/D50013

llvm-svn: 338324