Quiet ARI gettext checks

The ARI complains about this new file:

 common/signals-state-save-restore.c:46: warning: gettext: All messages should be marked up with _.
 common/signals-state-save-restore.c:59: warning: gettext: All messages should be marked up with _.
 common/signals-state-save-restore.c:87: warning: gettext: All messages should be marked up with _.
 common/signals-state-save-restore.c:92: warning: gettext: All messages should be marked up with _.

Since these are untranslatable strings, use () instead of _().

gdb/ChangeLog:
2016-08-10  Pedro Alves  <palves@redhat.com>

	* common/signals-state-save-restore.c
	(save_original_signals_state, restore_original_signals_state):
	Wrap perror_with_name arguments with '()'.