Use @llvm.objc.clang.arc.use intrinsic instead of clang.arc.use function.

Calls to this function are deleted in the ARC optimizer.  However when the ARC
optimizer was updated to use intrinsics instead of functions (r349534), the corresponding
clang change (r349535) to use intrinsics missed this one so it wasn't being deleted.

llvm-svn: 349782