tools headers UAPI: Sync case-sensitivity flags from linux/fs.h

tools headers UAPI: Sync case-sensitivity flags from linux/fs.h

The case-sensitivity series adds FS_XFLAG_CASEFOLD and
FS_XFLAG_CASENONPRESERVING to include/uapi/linux/fs.h, and
tools/perf/check-headers.sh would warn about the resulting drift
in the perf beauty copy.  Pick up only those two flags (and the
surrounding comment block) so the series does not introduce new
drift of its own.

This is not a full sync.  The perf copy is also missing the
FS_IOC_SHUTDOWN block added by commit 1f662195dbc0 ("fs: add
generic FS_IOC_SHUTDOWN definitions").  Because
tools/perf/check-headers.sh emits a single warning per file, that
warning will remain active until the older drift is picked up
too; closing it is left to a separate sync outside this series.

Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260507-case-sensitivity-v14-0-e62cc8200435@oracle.com?part=2
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://patch.msgid.link/20260515153515.362266-2-cel@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>