Add support for the MS qualifiers ptr32, ptr64, sptr, uptr.
This adds parsing of the qualifiers ptr32, ptr64, sptr, and uptr and
lowers them to the corresponding address space pointer for 32-bit and 64-bit pointers.
(32/64-bit pointers added in https://reviews.llvm.org/D69639)
A large part of this patch is making these pointers ignore the address space
when doing things like overloading and casting.
Reviewers: rnk, rsmith
Subscribers: jholewinski, jvesely, nhaehnle, cfe-commits
Differential Revision: https://reviews.llvm.org/D71039