cygwin: add statfs & fcntl

[Berrysoft]

Description

Needed by rustix support:

• statfs, fstatfs, and struct statfs
• posix_fadvise, posix_fallocate, fallocate, and constants

Sources

https://github.com/cygwin/cygwin/blob/8e2da4b223936bbf3329d5dd1658429b30b6d50d/winsup/cygwin/include/sys/vfs.h
https://github.com/cygwin/cygwin/blob/8e2da4b223936bbf3329d5dd1658429b30b6d50d/winsup/cygwin/include/fcntl.h

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

[rustbot]

r? @tgross35

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[tgross35]

LGTM!

@rustbot label +stable-nominated

[tgross35]

Updated the top post's links to permalinks, those are preferred in case implementations move/change