systemd: fix build against 6.9 libc-headers

systemd: fix build against 6.9 libc-headers

When building against the 6.9 linux-libc-headrs the following build
issue was hit:

  | Program check-filesystems.sh found: YES (build/tmp/work/cortexa57-poky-linux/systemd/255.4/git/src/basic/check-filesystems.sh)
  |
  | ../git/src/basic/meson.build:238:8: ERROR: Problem encountered: Unknown filesystems defined in kernel headers:
  |
  | Filesystem found in kernel header but not in filesystems-gperf.gperf: PID_FS_MAGIC

Upstream already has this fixed, so we backport the commit.

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>