In POSIX.1-2008, utime(3p) was marked as obsolescent in favor of
utimensat(2) and futimens(2). In the recent POSIX.1-2024 (Issue 8)
specification, <utime.h> and utime(3p) were officially removed.
utimensat(2) operates on `struct timespec` rather than the second-only
`struct utimbuf`, allowing sub-second timestamp updates while also
providing support for UTIME_NOW and UTIME_OMIT flags to selectively
update or preserve individual access and modification timestamps.
Introduce a compatibility layer for utimensat(2):
- Provide fallback definitions for AT_FDCWD, UTIME_NOW, and UTIME_OMIT
in case the system headers lack them.
- Introduce `ST_ATIME_NSEC(st)` to complement `ST_MTIME_NSEC(st)` and
`ST_CTIME_NSEC(st)`.
- Implement `git_utimensat()` in `compat/utimensat.c` as a fallback using
utimes(2) on platforms that define NO_UTIMENSAT.
- Implement `mingw_utimensat()` in `compat/mingw.c` converting `struct
timespec` to Windows FILETIME with 100ns precision.
- Wire up NO_UTIMENSAT support in Makefile, meson.build,
contrib/buildsystems/CMakeLists.txt, and configure.ac.
Subsequent commits will migrate callers across the codebase to
utimensat(2) and drop the legacy <utime.h> header.
Signed-off-by: Alexey Samsonov <vonosmas@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Alexey Samsonov