Thanks, does the attached (untested) patch fix things for you?
diff --git a/lib/acl-internal.h b/lib/acl-internal.h
index 11fdea1..d592a75 100644
--- a/lib/acl-internal.h
+++ b/lib/acl-internal.h
@@ -289,6 +289,10 @@ struct permission_context {
int get_permissions (const char *, int, mode_t, struct permission_context *);
int set_permissions (struct permission_context *, const char *, int);
-void free_permission_context (struct permission_context *);
+void free_permission_context (struct permission_context *)
+#if ! (defined USE_ACL && (HAVE_ACL_GET_FILE || defined GETACL))
+ _GL_ATTRIBUTE_CONST
+#endif
+ ;
_GL_INLINE_HEADER_END
