compilation issue on Arch

[Bruno Cornec]

In file included from include/busybox.h:8,
                 from applets/applets.c:9:
include/libbb.h:397:1: error: unknown type name ‘DIR’
  397 | DIR *xopendir(const char *path) FAST_FUNC;
      | ^~~
include/libbb.h:398:1: error: unknown type name ‘DIR’
  398 | DIR *warn_opendir(const char *path) FAST_FUNC;
      | ^~~
In file included from include/busybox.h:8,
                 from applets/applets.c:9:
include/libbb.h:1522:2: error: unknown type name ‘DIR’
 1522 |  DIR *dir;
      |  ^~~
In file included from <command-line>:
include/libbb.h:1523:26: error: unknown type name ‘DIR’
 1523 |  IF_FEATURE_SHOW_THREADS(DIR *task_dir;)
      |                          ^~~
./include/autoconf.h:3289:38: note: in definition of macro ‘IF_FEATURE_SHOW_THREADS’
 3289 | #define IF_FEATURE_SHOW_THREADS(...) __VA_ARGS__
      |                                      ^~~~~~~~~~~
make[1]: *** [scripts/Makefile.build:198: applets/applets.o] Error 1
make: *** [Makefile:372: applets_dir] Error 2
==> ERROR: A failure occurred in build().
    Aborting...