`Metadata::created()` not working on Linux with `statx`

[oxalica]

First of all, it now returns an Err with "not available on this platform currently".
But I found that there is a system call statx available in Linux kernel 4.11, which can get the birth time.

As the doc, the function uses stat on Unix platforms. But the stat result just never contains birthtime.

Shouldn't it try statx when available?