write-any-file: Don't reference an undefined function on native Windows

[Bruno Haible]

clang on native Windows shows a warning:

gllib\write-any-file.c(44,14): warning: implicit declaration of function 
'geteuid' is invalid in C99 [-Wimplicit-function-declaration]

geteuid does not exist on native Windows. Let's do like in tests/test-access.h.
This patch should fix the issue.


2024-08-27  Bruno Haible  <bruno@clisp.org>

        write-any-file: Don't reference an undefined function on native Windows.
        * m4/write-any-file.m4 (): Remove test for <priv.h>, obsolete since
        2009-05-03. Test for geteuid.
        * lib/write-any-file.c (geteuid): Define a fallback.

diff --git a/lib/write-any-file.c b/lib/write-any-file.c
index 27ca2c47c5..d1f98471a9 100644
--- a/lib/write-any-file.c
+++ b/lib/write-any-file.c
@@ -19,11 +19,18 @@
 
 #include <config.h>
 
+/* Specification.  */
 #include "write-any-file.h"
+
+#include <unistd.h>
+
 #include "priv-set.h"
 #include "root-uid.h"
 
-#include <unistd.h>
+/* mingw and MSVC 9 lack geteuid, so setup a dummy value.  */
+#if !HAVE_GETEUID
+# define geteuid() ROOT_UID
+#endif
 
 /* Return true if we know that we can write any file, including
    writing directories.  */
diff --git a/m4/write-any-file.m4 b/m4/write-any-file.m4
index 50e5aa0c2a..621d9b9e41 100644
--- a/m4/write-any-file.m4
+++ b/m4/write-any-file.m4
@@ -1,5 +1,5 @@
 # write-any-file.m4
-# serial 1
+# serial 2
 dnl Copyright (C) 2007, 2009-2024 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -11,5 +11,5 @@
 
 AC_DEFUN([gl_WRITE_ANY_FILE],
 [
-  AC_CHECK_HEADERS_ONCE([priv.h])
+  AC_CHECK_FUNCS_ONCE([geteuid])
 ])