Remove another use of AttributeWithIndex, using the AttributeSetImpl accessors instead.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173644 91177308-0d34-0410-b5e6-96231b3b80d8
Use proper type for the index.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173646 91177308-0d34-0410-b5e6-96231b3b80d8
Extracted ObjCARC.cpp into its own library libLLVMObjCARCOpts in preparation for refactoring the ARC Optimizer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173647 91177308-0d34-0410-b5e6-96231b3b80d8