Add UTIME_OMIT and UTIME_NOW

>This is NOT an issue, I am new to GitLab and don't find anything similar to discussions on GitHub, so I post it as an issue.

---

The futimens(2) syscall, which is used to update atime and mtime timestamps of a file, has two advantages over utimes(2), cite the man page from open group:

If the tv_nsec field of a timespec structure has the special value UTIME_NOW, the file's relevant timestamp shall be set to the greatest value supported by the file system that is not greater than the current time. If the tv_nsec field has the special value UTIME_OMIT, the file's relevant timestamp shall not be changed. In either case, the tv_sec field shall be ignored.

Redox does not seem to support these two features as there is no UTIME_NOW and UTIME_OMIT in relibc,

$ cd relibc
$ rg "UTIME_OMIT"

$ rg "UTIME_NOW"

Is there any plan to support these features? Yes.