[MS Demangler] Fix several issues related to templates.

These were uncovered when porting the mangling tests in
ms-templates.cpp from clang/CodeGenCXX over to demangling
tests.  The main issues fixed here are surrounding integer
literal signed and unsignedness, empty array dimensions,
and pointer and reference non-type template parameters.

Differential Revision: https://reviews.llvm.org/D50512

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@339434 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed