file-has-acl: avoid warning from bleeding-edge GCC

* lib/file-has-acl.c: Include attribute.h.
(have_xattr): Declare with ATTRIBUTE_PURE,
to avoid new warning from GCC14-to-be.
* modules/file-has-acl (Depends-on): Add attribute.
Spotted while building coreutils with this:
gcc version 14.0.0 20230526 (experimental)

ChangeLog

@@ -1,3 +1,13 @@
+2023-05-28  Jim Meyering  <meyering@fb.com>
+
+	file-has-acl: avoid warning from bleeding-edge GCC
+	* lib/file-has-acl.c: Include attribute.h.
+	(have_xattr): Declare with ATTRIBUTE_PURE,
+	to avoid new warning from GCC14-to-be.
+	* modules/file-has-acl (Depends-on): Add attribute.
+	Spotted while building coreutils with this:
+	gcc version 14.0.0 20230526 (experimental)
+
 2023-05-28  Bruno Haible  <bruno@clisp.org>
 
 	error: Avoid -Wint-in-bool-context warning.

lib/file-has-acl.c

@@ -28,7 +28,7 @@
 #include "acl.h"
 
 #include "acl-internal.h"
-
+#include "attribute.h"
 #include "minmax.h"
 
 #if USE_ACL && HAVE_LINUX_XATTR_H && HAVE_LISTXATTR
@@ -50,7 +50,7 @@ enum {
 /* Return true if ATTR is in the set represented by the NUL-terminated
    strings in LISTBUF, which is of size LISTSIZE.  */
 
-static bool
+ATTRIBUTE_PURE static bool
 have_xattr (char const *attr, char const *listbuf, ssize_t listsize)
 {
   char const *blim = listbuf + listsize;

modules/file-has-acl

@@ -8,6 +8,7 @@ m4/acl.m4
 
 Depends-on:
 acl-permissions
+attribute
 extern-inline
 minmax
 free-posix