selftests/fs/mount-notify: Fix compilation failure.

Commit c6d9775c20 ("selftests/fs/mount-notify: build with tools include
dir") introduces the struct __kernel_fsid_t to decouple dependency with
headers_install.  The commit forgets to define a macro for __kernel_fsid_t
and it will cause type re-definition issue.

Signed-off-by: Xing Guo <higuoxing@gmail.com>
Link: https://lore.kernel.org/20250813031647.96411-1-higuoxing@gmail.com
Acked-by: Amir Goldstein <amir73il@gmail.com>
Closes: https://lore.kernel.org/oe-lkp/202508110628.65069d92-lkp@intel.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

tools/testing/selftests/filesystems/mount-notify/mount-notify_test.c

@@ -2,6 +2,13 @@
 // Copyright (c) 2025 Miklos Szeredi <miklos@szeredi.hu>
 
 #define _GNU_SOURCE
+
+// Needed for linux/fanotify.h
+typedef struct {
+	int	val[2];
+} __kernel_fsid_t;
+#define __kernel_fsid_t __kernel_fsid_t
+
 #include <fcntl.h>
 #include <sched.h>
 #include <stdio.h>
@@ -10,20 +17,12 @@
 #include <sys/mount.h>
 #include <unistd.h>
 #include <sys/syscall.h>
+#include <sys/fanotify.h>
 
 #include "../../kselftest_harness.h"
 #include "../statmount/statmount.h"
 #include "../utils.h"
 
-// Needed for linux/fanotify.h
-#ifndef __kernel_fsid_t
-typedef struct {
-	int	val[2];
-} __kernel_fsid_t;
-#endif
-
-#include <sys/fanotify.h>
-
 static const char root_mntpoint_templ[] = "/tmp/mount-notify_test_root.XXXXXX";
 
 static const int mark_cmds[] = {

tools/testing/selftests/filesystems/mount-notify/mount-notify_test_ns.c

@@ -2,6 +2,13 @@
 // Copyright (c) 2025 Miklos Szeredi <miklos@szeredi.hu>
 
 #define _GNU_SOURCE
+
+// Needed for linux/fanotify.h
+typedef struct {
+	int	val[2];
+} __kernel_fsid_t;
+#define __kernel_fsid_t __kernel_fsid_t
+
 #include <fcntl.h>
 #include <sched.h>
 #include <stdio.h>
@@ -10,21 +17,12 @@
 #include <sys/mount.h>
 #include <unistd.h>
 #include <sys/syscall.h>
+#include <sys/fanotify.h>
 
 #include "../../kselftest_harness.h"
-#include "../../pidfd/pidfd.h"
 #include "../statmount/statmount.h"
 #include "../utils.h"
 
-// Needed for linux/fanotify.h
-#ifndef __kernel_fsid_t
-typedef struct {
-	int	val[2];
-} __kernel_fsid_t;
-#endif
-
-#include <sys/fanotify.h>
-
 static const char root_mntpoint_templ[] = "/tmp/mount-notify_test_root.XXXXXX";
 
 static const int mark_types[] = {