Add support for MIPS targets

[gabrielesvelto]

Closes #300

[gabrielesvelto]

I've slightly reorganized the code dealing with CPU sets so that ARM and MIPS have a CPU_SETSIZE limited to 32 only under Android (i.e. when using bionic) but use the full Linux CPU_SETSIZE otherwise. To work correctly this also needs a fix to the libc crate which I've pushed here: rust-lang/libc#217

[posborne]

Awesome, MIPS/MIPSEL are targets that will be tested (at least for compilation) when #297 (or whatever follows and integrates with travis) lands.

I'll hold off on approving until the changes in libc are published. If we can get the CI changes in places and merged in soonish @humu can check that everything works.

[gabrielesvelto]

The change to libc has landed and it's available in version 0.2.8 of the crate: rust-lang/libc@2278a54

[gabrielesvelto]

The dependency in libc has landed, is there anything else needed before this can be merged?

[kamalmarhubi]

@homu r+

@posborne I figure we can fix any issues that come up in CI when we turn it on.

[homu]

📌 Commit 86b3cfa has been approved by kamalmarhubi

[homu]

⌛ Testing commit 86b3cfa with merge d53950a...

[homu]

☀️ Test successful - status