bitrig support

[dhuseby]

This adds Bitrig support to the version of jemalloc (b001609) currently used by Rust.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @nikomatsakis (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see CONTRIBUTING.md for more information.

[alexcrichton]

Have you tried sending this upstream to jemalloc as well? In general we try to be sure to land all patches there first before our own repos, and it looks like they'd be quite welcoming of this!

[dhuseby]

@alexcrichton I am upstreaming this patch here.

[dhuseby]

@alexcrichton this change was just upstreamed to jemalloc: jemalloc@970fcfb

[alexcrichton]

Yay! Can you make a new PR with the included changes?