Consider reference, pointer, and pointer-to-member TemplateArguments to be different...

Consider reference, pointer, and pointer-to-member TemplateArguments to be different if they have different types.

For the Itanium ABI, this implements the mangling rule suggested in
https://github.com/itanium-cxx-abi/cxx-abi/issues/47, namely mangling
such template arguments as being cast to the parameter type in the case
where the template name is overloadable. This can cause a mangling
change for rare cases, where

 * the template argument declaration is converted from its declared type
   to the type of the template parameter, and
 * the template parameter either has a deduced type or is a parameter of
   a function template.

However, such changes are necessary to avoid mangling collisions. The
ABI changes can be reversed with -fclang-abi-compat=11 or earlier.

Re-commit with a fix for a couple of regressions.

Differential Revision: https://reviews.llvm.org/D91488