Use FPT::getArgTypes() instead of manually building ArrayRefs

Made significantly easier with git-clang-format.

Differential Revision: http://llvm-reviews.chandlerc.com/D947

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@183694 91177308-0d34-0410-b5e6-96231b3b80d8
cleanup (address some more review comments for r183474):
- reduce default buffer size to 64, which will still be large enough to
  hold any property names found in the wild.
- get rid of the /*static*/ comments.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@183697 91177308-0d34-0410-b5e6-96231b3b80d8