Move js to libc from crates.io.

[Ms2ger]

Requires servo/rust-mozjs#136.

[hoppipolla-critic-bot]

Critic review: https://critic.hoppipolla.co.uk/r/4021

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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.

[jdm]

r+

[jdm]

@bors: retry

• servo#4041

[bors-servo]

saw approval from jdm
at Ms2ger@63f6063

[bors-servo]

merging Ms2ger/servo/js-libc = 63f6063 into auto

[bors-servo]

Ms2ger/servo/js-libc = 63f6063 merged ok, testing candidate = 9e2d587

[bors-servo]

some tests failed:
failure: http://build.servo.org/builders/linux2/builds/780

[bors-servo]

saw approval from jdm
at Ms2ger@63f6063

[bors-servo]

merging Ms2ger/servo/js-libc = 63f6063 into auto

[bors-servo]

Ms2ger/servo/js-libc = 63f6063 merged ok, testing candidate = d94bd27

[bors-servo]

all tests pass:
success: http://build.servo.org/builders/linux1/builds/784
success: http://build.servo.org/builders/linux2/builds/782
success: http://build.servo.org/builders/android/builds/818
success: http://build.servo.org/builders/mac1/builds/999
success: http://build.servo.org/builders/mac2/builds/999

[bors-servo]

fast-forwarding master to auto = d94bd27