Fix a couple of mangling canonicalizer corner case bugs.

Summary:
The hash computed for an ArrayType was different when first constructed
versus when later profiled due to the constructor default argument, and
we were not tracking constructor / destructor variant as part of the
mangled name AST, leading to incorrect equivalences.

Reviewers: erik.pilkington

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D51463

llvm-svn: 342166