busybox: Fix in-store invocation of busybox

This fixes the usage for stdenv bootstrap.

Additionally, dezgeg ported the patch from 1.25.1 to 1.26.1

pkgs/os-specific/linux/busybox/busybox-in-store.patch

···
  		exit(busybox_main(argv));
  #  endif
  #  if NUM_APPLETS > 0
+@@ -981,7 +981,7 @@ int main(int argc UNUSED_PARAM, char **argv)
+ 
+ 	lbb_prepare("busybox" IF_FEATURE_INDIVIDUAL(, argv));
+ # if !ENABLE_BUSYBOX
+-	if (argv[1] && is_prefixed_with(bb_basename(argv[0]), "busybox"))
++	if (argv[1] && strstr(bb_basename(argv[0]), "busybox") != 0)
+ 		argv++;
+ # endif
+ 	applet_name = argv[0];