(macOS) When rewriting the dylib identifier and paths to linked
libraries in a collected binary, instead of directly using
@loader_path-based path, use @rpath-based path and replace
rpaths in the binary with a single rpath that points to the top-level
application directory, relative to @loader_path. This ensures that
the library identifiers of collected shared libraries and their
references in referring binaries always match, which allows packages
to pre-load a library from an arbitrary location via for example
ctypes.