[ms-cxxabi] Fix a number of bugs in the mangler.

This includes the following fixes:
 - Implement 4 subtly different variants of qualifier mangling and use them
   in what I believe are the right places.
 - Fix handling of array types.  Previously we were always decaying them,
   which is wrong if the type appears as a template argument, pointee,
   referent etc.
Fixes PR13182.

Differential Revision: http://llvm-reviews.chandlerc.com/D709