The files in this directory are copied from current kernel master
(b06ed1e7a2fa9b636f368a9e97c3c8877623f8b2) or WireGuard master
(8416093498ac2c754536dad4757c5d86c9ba8809), and the following
modifications are applied:
- btrfs.h: drop '__user' attributes
- if.h: drop '#include <linux/compiler.h>' and '__user' attributes
- stddef.h: drop '#include <linux/compiler_types.h>'
- guard linux/fs.h include to avoid conflict with glibc 2.36
