Improve handling of __FUNCTION__ and other predefined expression for Objective-C Blocks

Instead of always displaying the mangled name, try to do better
and get something closer to regular functions.

Recommit r287039 (that was reverted in r287039) with a tweak to
be more generic, and test fixes!

Differential Revision: https://reviews.llvm.org/D26522

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@287085 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed