gpg: Use sigdescr_np for newer GNU C library.
* g10/signal.c (got_fatal_signal): 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>