osxuniversalgenerator: Work around Meson assuming absolute dylib IDs
This works around an undocumented semantic in Meson as regard dylibs' IDs. The fix performed for dyld in 2c058e57 meant that anyone attempting to use relocated libraries within Meson would have their libraries or executables crash at launch, since Meson does not insert any RPATH entries for dependencies, only for build targets in the current project.
See:
!1478 (merged) https://github.com/mesonbuild/meson/pull/3691