lib/fileutils: add ul_basename()

lib/fileutils: add ul_basename()

Unfortunately, the basename() function can be affected by the
creativity of different libc authors, resulting in varying behavior
across implementations.

Instead, use a local implementation to ensure consistency and
portability.

Signed-off-by: Karel Zak <kzak@redhat.com>
(cherry picked from commit ff8ee29d648111eb222612ad4251e4c3b236a389)