Since Mach-O has a two-level namespace (unlike ELF), we can usually set
this property to true.
(I believe this setting is only available in the new LTO backend, so I
can't really use ld64 / libLTO's behavior as a reference here... I'm
just doing what I think is correct.)
See {D119294} for the work done to calculate the `interposable` used in
this diff.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D119506
Jez Ng