Android fixes for February Rust Upgrade

DO NOT MERGE (not that you could, as it needs a rebase).

This contains the required fixes for Android. All of the submodules but the rust compiler should land in the main servo repositories shortly; the rust compiler revision is on remote https://github.com/larsbergstrom/rust.git. 

The only major code change here is that #[thread_local] variables are not supported on Android, so I had to implement them the slow way with local_data instead.

@aydinkim This should implement everything except for the fontconfig issue I mentioned during the recent Servo meeting, where it gives an error about missing fontconfig global configuration file.