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/fflush_stdout_and_exit.c

@@ -13,13 +13,17 @@
 
 #include "libbb.h"
 
-// TODO: make it safe to call from NOFORK applets
-// Currently, it can exit(0). Even if it is made to do longjmp trick
-// (see sleep_and_die internals), zero cannot be passed thru this way!
-
 void fflush_stdout_and_exit(int retval)
 {
 	if (fflush(stdout))
-		sleep_and_die();
+		xfunc_die();
+
+	if (ENABLE_FEATURE_EXEC_PREFER_APPLETS && die_sleep < 0) {
+		/* We are in NOFORK applet. Do not exit() directly,
+		 * but use xfunc_die() */
+		xfunc_error_retval = retval;
+		xfunc_die();
+	}
+
 	exit(retval);
 }