llvm/ObjCARC: Split OptimizeIndividualCallImpl out of OptimizeIndividualCalls, NFC
Split out a helper function for the individual call optimizations and
skip useless calls to it (where the instruction is not an ARC
intrinsic). Besides reducing indentation (and possibly speeding up
compile time in some small way), an upcoming patch will add additional
calls and expand out the switch.
(cherry picked from commit 783cb86b616d9de59213ea17649d6e2df8c1ebbb)