target-finalize: do not strip libthread_db

Fix previous commit not to strip libthread_db library. In the previous
commit the wildcard was incorrectly matching the symbolic link instead
of the real library file.

Signed-off-by: Javier Viguera <javier.viguera@digi.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>