nommu: fix cases where we mangle argv[0][0]

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

include/libbb.h

@@ -981,6 +981,9 @@ enum {
 # define bb_daemonize(flags)                bb_daemonize_or_rexec(flags, bogus)
 #else
   extern bool re_execed;
+  /* Note: re_exec() and fork_or_rexec() do argv[0][0] |= 0x80 on NOMMU!
+   * _Parent_ needs to undo it if it doesn't want to have argv[0] mangled.
+   */
   void re_exec(char **argv) NORETURN FAST_FUNC;
   pid_t fork_or_rexec(char **argv) FAST_FUNC;
   int  BUG_fork_is_unavailable_on_nommu(void) FAST_FUNC;