Use some form of iterative deepening with early return in
`find_libraries`:
1. Search `<root>`, `<root>/{lib, lib64,...}` dirs at max depth 0 and
return early if found.
2. Search `<root>/{lib, lib64,...}` dirs at max depth 1 and return early
if found (covers e.g. `<root>/lib/x86_64-linux-gnu/` subdirs)
3. Fall back to exhaustive search up to `max_depth - 1` of
`<root>/{lib, lib64, ...}`.
Set the default library search handler of `max_depth` to `4` to still
cover `<root>/lib/pythonX.Y/site-packages/<name>/`.
0ec918570a