- most importantly, fix a use-after-free when using thin archives,
by putting the archive unique_ptr to the arena allocator. This
ports D65565 to MachO
- correctly demangle symbol namess from archives in diagnostics
- add a test for thin archives -- it finds this UaF, but only when
running it under asan (it also finds the demangling fix)
- make forceLoadArchive() use addFile() with a bool to have the archive
loading code in fewer places. no behavior change; matches COFF port a
bit better
Differential Revision: https://reviews.llvm.org/D92360
Nico Weber