XDG needs <signal.h>

Reported-by: Joseph Atkinson <jsa@freebsd.org>
(cherry picked from commit ad81f3760bba308ba33f52eb12abbdb43ebc296e)

modules/misc/inhibit/xdg.c

@@ -26,6 +26,7 @@
 #include <vlc_plugin.h>
 #include <vlc_inhibit.h>
 #include <assert.h>
+#include <signal.h>
 #include <spawn.h>
 #include <sys/wait.h>