backends/backends: recurse when looking for paths in bundled shared libraries
backends/backends: recurse when looking for paths in bundled shared libraries

This previously worked because we were accidentally doing this via
mutation. However, doing this via mutation is not a good way to do it,
we should be explicit.

Fixes #9542

mesonbuild/meson,mesonbuild/meson,pexip/meson,pexip/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson