[ms-cxxabi] Mangle in an implicit 'E' for certain types on win64

Most of the complexity of this patch is figuring out which types get the
qualifier and which don't.  If we implement __ptr32/64, then we should
check the qualifier instead of assuming all pointers are 64-bit.

This fixes PR13792.

Patch by Warren Hunt!

llvm-svn: 181825