Fix bugs on mingw when module dirfd is in use

[Bruno Haible]

Building gettext on mingw, I see these warnings:

gettext-tools/gnulib-lib/getcwd.c:293:36: warning: passing argument 1 of 
'closedir' from incompatible pointer type [-Wincompatible-pointer-types]
gettext-tools/gnulib-lib/getcwd.c:311:17: warning: assignment from incompatible 
pointer type [-Wincompatible-pointer-types]
gettext-tools/gnulib-lib/getcwd.c:507:32: warning: passing argument 1 of 
'closedir' from incompatible pointer type [-Wincompatible-pointer-types]
gettext-tools/gnulib-lib/getcwd.c:541:19: warning: passing argument 1 of 
'closedir' from incompatible pointer type [-Wincompatible-pointer-types]

The cause is that the 'dirfd' support for native Windows (from 2023-04-26)
overrides DIR and all related functions. But the code in getcwd.c undefines
only opendir and closedir. The net result is that getcwd.o depends on the
functions opendir, closedir, rpl_readdir, rpl_rewinddir; this will not work
at runtime, since the overridden DIR is not pointer-compatible with the
original DIR.

This patch fixes it.


2023-06-05  Bruno Haible  <bruno@clisp.org>

        Fix bugs on mingw when module dirfd is in use (regression 2023-04-26).
        * lib/getcwd.c: When GNULIB_defined_DIR, revert to the system's
        definitions of opendir, closedir, readdir, rewinddir.
        * lib/mountlist.c: When GNULIB_defined_DIR, revert to the system's
        definitions of opendir, closedir, readdir.
        * lib/scandir.c: Likewise.
        * lib/glob.c: Fix comment. When GNULIB_defined_DIR, don't undefine
        opendir, closedir.

diff --git a/lib/getcwd.c b/lib/getcwd.c
index 0530630c43..28f69133a8 100644
--- a/lib/getcwd.c
+++ b/lib/getcwd.c
@@ -114,13 +114,21 @@
    FIXME - if the kernel ever adds support for multi-thread safety for
    avoiding standard fds, then we should use opendir_safer and
    openat_safer.  */
-#ifdef GNULIB_defined_opendir
+#ifdef GNULIB_defined_DIR
+# undef DIR
 # undef opendir
-#endif
-#ifdef GNULIB_defined_closedir
 # undef closedir
+# undef readdir
+# undef rewinddir
+#else
+# ifdef GNULIB_defined_opendir
+#  undef opendir
+# endif
+# ifdef GNULIB_defined_closedir
+#  undef closedir
+# endif
 #endif
-
+
 #if defined _WIN32 && !defined __CYGWIN__
 # if HAVE_MSVC_INVALID_PARAMETER_HANDLER
 static char *
diff --git a/lib/glob.c b/lib/glob.c
index ddca1e9820..af0694eec4 100644
--- a/lib/glob.c
+++ b/lib/glob.c
@@ -182,16 +182,17 @@ convert_dirent64 (const struct dirent64 *source)
 #endif
 
 #ifndef _LIBC
-/* The results of opendir() in this file are not used with dirfd and fchdir,
-   and we do not leak fds to any single-threaded code that could use stdio,
-   therefore save some unnecessary recursion in fchdir.c and opendir_safer.c.
-   FIXME - if the kernel ever adds support for multi-thread safety for
-   avoiding standard fds, then we should use opendir_safer.  */
-# ifdef GNULIB_defined_opendir
-#  undef opendir
-# endif
-# ifdef GNULIB_defined_closedir
-#  undef closedir
+/* The results of opendir() in this file are used with dirfd.  But they are
+   not used with fchdir, and we do not leak fds to any single-threaded code
+   that could use stdio, therefore save some unnecessary recursion in
+   fchdir.c and opendir_safer.c.  */
+# ifndef GNULIB_defined_DIR
+#  ifdef GNULIB_defined_opendir
+#   undef opendir
+#  endif
+#  ifdef GNULIB_defined_closedir
+#   undef closedir
+#  endif
 # endif
 
 /* Just use malloc.  */
diff --git a/lib/mountlist.c b/lib/mountlist.c
index 6d38481284..8b06e7b7ee 100644
--- a/lib/mountlist.c
+++ b/lib/mountlist.c
@@ -154,11 +154,18 @@
 
 /* The results of opendir() in this file are not used with dirfd and fchdir,
    therefore save some unnecessary work in fchdir.c.  */
-#ifdef GNULIB_defined_opendir
+#ifdef GNULIB_defined_DIR
+# undef DIR
 # undef opendir
-#endif
-#ifdef GNULIB_defined_closedir
 # undef closedir
+# undef readdir
+#else
+# ifdef GNULIB_defined_opendir
+#  undef opendir
+# endif
+# ifdef GNULIB_defined_closedir
+#  undef closedir
+# endif
 #endif
 
 #define ME_DUMMY_0(Fs_name, Fs_type)            \
diff --git a/lib/scandir.c b/lib/scandir.c
index 9d582e7ac3..429067ed74 100644
--- a/lib/scandir.c
+++ b/lib/scandir.c
@@ -62,8 +62,19 @@
    therefore save some unnecessary recursion in fchdir.c and opendir_safer.c.
    FIXME - if the kernel ever adds support for multi-thread safety for
    avoiding standard fds, then we should use opendir_safer.  */
-# undef opendir
-# undef closedir
+# ifdef GNULIB_defined_DIR
+#  undef DIR
+#  undef opendir
+#  undef closedir
+#  undef readdir
+# else
+#  ifdef GNULIB_defined_opendir
+#   undef opendir
+#  endif
+#  ifdef GNULIB_defined_closedir
+#   undef closedir
+#  endif
+# endif
 #endif
 
 #ifndef SCANDIR_CANCEL