tree-wide: Make sure all headers are standalone

Let's make sure all of our headers include everything they require.

src/basic/missing_xfs.h

@@ -1,6 +1,8 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
+#include <stdint.h>
+
 /* This is currently not exported in the public kernel headers, but the libxfs library code part of xfsprogs
  * defines it as public header */