Add DragonFly toolchain

[mneumann]

This sets up the toolchain (binutils, gcc, libraries) needed for cross-compiling to DragonFly.
Note that bsdtar is required to unpack the DragonFly ISO image, as there are no .tar.gz releases of DragonFly.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @brson (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. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed.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 the contribution instructions for more information.

[alexcrichton]

Do you have links for where these patches come from? Just so if we need to update this we know where to look

[mneumann]

they are from DragonFly's dports collection (dports =~ FreeBSD ports): https://github.com/DragonFlyBSD/DeltaPorts/tree/master/ports/lang/gcc5/dragonfly or https://github.com/DragonFlyBSD/DPorts/tree/master/lang/gcc5. DeltaPorts is our layer above FreeBSD's ports collection. DPorts is then created by applying the patches from DeltaPorts against FreeBSD's ports.

[mneumann]

I think you only need to update the patches in case you change the gcc version. Newer versions of gcc might already ship with those patches.

[alexcrichton]

Thanks for the info! Could you add that as a comment here? We may need to update gcc one day and it'd just be good to know where the patches came from so we could perhaps pick up others if they're necessary.

[mneumann]

@alexcrichton Have added a comment.

[alexcrichton]

Thanks!

To confirm as well, have you built a toolchain inside of the container and confirmed that it works locally on DragonFly as well?

[mneumann]

@alexcrichton I can confirm that I can cross-compile a DragonFly executable from within the container, which later can be executed on a recent DragonFly system. I only tested a simple hello world application written in C. For this, file returns:

/tmp/t: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /usr/libexec/ld-elf.so.2, for DragonFly 4.0.400, not stripped

What I haven't done yet is to build a rust toolchain from within the container. This sounds a little bit more complicated.

[alexcrichton]

Ok, once that's working just let me know! Then we can work on getting nightlies for DragonFly as well