[c++1z] Fixes for generalized non-type template argument support: check for
exact type match for deduced template arguments, and be sure to produce correct
canonical TemplateArgument representations to enable correct redeclaration
matching.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@224456 91177308-0d34-0410-b5e6-96231b3b80d8