[objc-arc] Cleaned up tail-call-invariant-enforcement.ll.

Specifically:

1. Added checks that unwind is being properly added to various instructions.
2. Fixed the declaration/calling of objc_release to have a return type of void.
3. Moved all checks to precede the functions and added checks to ensure that the
checks would only match inside the specific function that we are attempting to
check.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179973 91177308-0d34-0410-b5e6-96231b3b80d8