[ObjC][ARC] Convert the retainRV marker that is passed as a named
metadata into a module flag in the auto-upgrader and make the ARC
contract pass read the marker as a module flag.
This is needed to fix a bug where ARC contract wasn't inserting the
retainRV marker when LTO was enabled, which caused objects returned
from a function to be auto-released.
Differential Revision: https://reviews.llvm.org/D60303