Change the objc ARC optimizer to use the new objc.* intrinsics

We're moving ARC optimisation and ARC emission in clang away from runtime methods
and towards intrinsics.  This is the part which actually uses the intrinsics in the ARC
optimizer when both analyzing the existing calls and emitting new ones.

Differential Revision: https://reviews.llvm.org/D55348

Reviewers: ahatanak
llvm-svn: 349534