Add statx linux system call so we can implement fs::Metadata::created on Linux

[ariasuni]

Right now, std::fs::Metadata::created returns an Err on Linux. But the creation time is available with the statx system call.

https://unix.stackexchange.com/a/407305/289105

[alexcrichton]

Should be fine to send a PR to add this API!

[gnzlbg]

We haven't added other syscalls in the past (e.g. memfd_create: #902 (comment)). There is nothing blocking using this syscall in std::fs btw, you can just use syscall to call it yourselfe, like, e.g., I did with memfd_create here: https://github.com/gnzlbg/slice_deque/blob/master/src/mirrored/linux.rs#L18

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EDIT: e.g. in the docs of statx it says:

There is no glibc wrapper for statx(); see NOTES.

such that the only easy way to call it is using syscall anyways. If there isn't a const for doing this call, we should probably expose that constant here though.

[ariasuni]

@gnzlbg There is a statx() wrapper in glibc but the man page is not up-to-date (fixed upstream but not yet released).

I’m not sure what’s the best way to access the creation information under Linux (if I want to implement a workaround in the meantime), since you mentioned using the syscall directly (note btw that there’s no SYS_statx in the libc crate).

[gnzlbg]

There does not seem to be any open rust-lang/rust issues about this.