Enable 32bit builds.

[metajack]

You specify a 32bit build by setting --target on configure.

Depends on servo/rust-mozjs#77

[hoppipolla-critic-bot]

Critic review: https://critic.hoppipolla.co.uk/r/1429

This is an external review system which you may optionally use for the code review of your pull request.

In order to help critic track your changes, please do not make in-place history rewrites (e.g. via git rebase -i or git commit --amend) when updating this pull request.

[metajack]

This is ready for review now. Critic isn't happy about my force pushes, so please review in GitHub. r? @larsberg or @jdm

[larsberg]

I think you've got the wrong lars berg, good luck with the review though

[jdm]

You'll need to push your latest rust-mozjs changes.

[metajack]

Sorry @larsberg! I meant @larsbergstrom.

@jdm rust-mozjs is pushed and awaiting your review.

[larsbergstrom]

@metajack Did you verify that this doesn't break Android builds? (or at least not break them any further )

[metajack]

Ok, this is ready to review and to land. All the submodules are landed except for the minor rust-phf update.

r? @larsbergstrom