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  K&R C signal(2) signature is obsolete.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>

libmisc/loginprompt.c

@@ -41,9 +41,9 @@ void login_prompt (const char *prompt, char *name, int namesize)
 	int i;
 	FILE *fp;
 
-	RETSIGTYPE (*sigquit) (int);
+	sighandler_t sigquit;
 #ifdef	SIGTSTP
-	RETSIGTYPE (*sigtstp) (int);
+	sighandler_t sigtstp;
 #endif
 
 	/*