Refactored out pass ObjCARCAPElim from ObjCARCOpts.cpp => ObjCARCAPElim.cpp.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173654 91177308-0d34-0410-b5e6-96231b3b80d8
Revert r173646, "Use proper type for the index."

Unfortunately, msvc miscompiles it. Investigating.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173656 91177308-0d34-0410-b5e6-96231b3b80d8