make standalone httpd work on NOMMU machines

include/libbb.h

@@ -587,10 +587,12 @@ enum {
 };
 #if BB_MMU
   void forkexit_or_rexec(void);
+  enum { re_execed = 0 };
 # define forkexit_or_rexec(argv)            forkexit_or_rexec()
 # define bb_daemonize_or_rexec(flags, argv) bb_daemonize_or_rexec(flags)
 # define bb_daemonize(flags)                bb_daemonize_or_rexec(flags, bogus)
 #else
+  void re_exec(char **argv) ATTRIBUTE_NORETURN;
   void forkexit_or_rexec(char **argv);
   extern bool re_execed;
 # define fork()          BUG_fork_is_unavailable_on_nommu()