objective-C arc IR-gen. Retaining of strong
arguments in function prologue is done
with objc_StoreStrong to pair it with
similar objc_StoreStrong for release in function
epilogue. This is done with -O0 only.
// rdar://13145317


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175698 91177308-0d34-0410-b5e6-96231b3b80d8