Use 'void' instead of 'RETSIGTYPE'. Use 'sighandler_t' too.

C89 and POSIX.1-2001 define signal(2) as returning a pointer to a
function returning 'void'.  K&R C signal(2) signature is obsolete.
Use 'void' directly.

Also, instead of writing the function pointer type explicitly, use
POSIX's 'sighandler_t'.

Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>

src/sulogin.c

@@ -44,9 +44,9 @@ extern char **environ;
 #endif
 
 /* local function prototypes */
-static RETSIGTYPE catch_signals (int);
+static void catch_signals (int);
 
-static RETSIGTYPE catch_signals (unused int sig)
+static void catch_signals (unused int sig)
 {
 	_exit (1);
 }