Linux: add reboot() and constants

[bugaevc]

Add declarations from sys/reboot.h and linux/reboot.h. Initially originated as nix-rust/nix#386.

[rust-highfive]

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[bugaevc]

Should the rest of reboot declarations be in notbsd/mod.rs, or should I copy the declarations to notbsd/android, or are they somehow included from notbsd/linux/mod.rs (doesn't seem to be the case, but there are lots of functions there and just several in notbsd/android)?

[alexcrichton]

If they're shared among all the platforms under notbsd (Android + Linux) then it should be fine to place the definitions in notbsd/mod.rs, but copying is also fine. Looks like CI is green here so I'd be good merging, but do you wanna juggle around the declarations a bit?

[bugaevc]

I'm not really sure whether the same stuff is available under Android: Android is Linux anyway, but it may well be glibc-specific stuff.
Let me try to put them into notbsd and see if that breaks the Android build.

[bugaevc]

OK, so it does break the Android build. Reverting.

[bugaevc]

Feel free to merge this (or should we play the rebasing/squashing game?).

[alexcrichton]

Nah this is fine, thanks again!

[bugaevc]

Thanks! When can I expect this to be released (e.g. to use it in nix)?

[alexcrichton]

Would it be possible for nix to use a git version of libc for now? I can be sure to make a release right before a nix release, but we just made a release yesterday I believe for another nix-requested PR :)

[alexcrichton]

That being said, I certainly don't mind making another release!

[bugaevc]

Filed nix-rust/nix#387 for nix to track libc's master

[alexcrichton]

Thanks! I'll add some comments over there as well.