common: Fix get_signal_name for GNU/Linux.
* common/signal.c (get_signal_name): Use sigdescr_np if available. * configure.ac: Check the function.
Backport master commit of:
c4ba712736ddeda66055567874d573e79d22666b
- GnuPG-bug-id: T5568
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>