make a few struct bb_applet members conditional

rename sllep_and_die -> xfunc_die
make fflush_stdout_and_exit NOFORK-safe
fix some buglets found by randomconfig

libbb/herror_msg_and_die.c

@@ -7,9 +7,6 @@
  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
  */
 
-#include <stdarg.h>
-#include <stdlib.h>
-
 #include "libbb.h"
 
 void bb_herror_msg_and_die(const char *s, ...)
@@ -19,5 +16,5 @@ void bb_herror_msg_and_die(const char *s, ...)
 	va_start(p, s);
 	bb_vherror_msg(s, p);
 	va_end(p);
-	sleep_and_die();
+	xfunc_die();
 }