Add an AdjustedType sugar node for adjusting calling conventions

Add an AdjustedType sugar node for adjusting calling conventions

Summary:
In general, this type node can be used to represent any type adjustment
that occurs implicitly without losing type sugar.  The immediate use of
this is to adjust the calling conventions of member function pointer
types without breaking template instantiation.

Fixes PR17996.

Reviewers: rsmith

Differential Revision: http://llvm-reviews.chandlerc.com/D2332

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@196451 91177308-0d34-0410-b5e6-96231b3b80d8