Fix stat definition for android aarch64

[malbarbo]

libc::stat for android aarch64 was change in rust-lang/libc#538, this PR update raw::stat to match libc::stat. libc is now tested on aarch64 android, so libc::stat should be correct.

Also changed nlink_t to u64 on x86_64 to match the others android archs (and to satisfy #31551)

[rust-highfive]

r? @brson

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[malbarbo]

r? @alexcrichton

[alexcrichton]

Hm so one reason this whole module is deprecated is that a number of the definitions are known to be incorrect. Is there motivation for correcting them? In theory no code is using these bindings...

[malbarbo]

My motivation is to make it correct... Maybe there are some one using it in the wild. When I read #31551 I thought that std::os::*::raw::*_t could be incorrect, but stat should be correct.

The main problem here is that stat can give wrong results (even segfault if the size is different from libc::stat). The others raw::*_t types do not have these problems.

Is there any problem in making it correct?

[alexcrichton]

The main thing I'm worried about is breaking code which may inadvertently be working today, unfortunately. My guess is that most code, if using this at all, is broken anyway, though. I just personally lean towards not bothering with these modules as they shouldn't be used anyway and fixing them can require nontrivial effort.

[malbarbo]

Ok. Thanks.