fs_shell: Add stub wait_for_thread.

We already have a dummy spawn_kernel_thread, so this makes sense to add
(and will be required by the next commit.)

Change-Id: Ic46607d46dabc6fd46fcfc0b6f8da0ed9897cfc9
Reviewed-on: https://review.haiku-os.org/c/1650
Reviewed-by: waddlesplash <[email protected]>

src/tools/fs_shell/kernel_export.cpp

@@ -21,6 +21,13 @@ fssh_spawn_kernel_thread(fssh_thread_func function, const char *threadName,
 }
 
 
+fssh_status_t
+fssh_wait_for_thread(fssh_thread_id thread, fssh_status_t *_returnCode)
+{
+	return FSSH_B_ERROR;
+}
+
+
 fssh_status_t
 fssh_user_memcpy(void *dest, const void *source, fssh_size_t length)
 {