Add sanitizer support to cross

[gnzlbg]

Instead of going through xargo it would be great if cross could, at least for x86_64-unknown-linux-gnu, compile projects with a std library compiled with sanitizer support and optionally also run the tests with sanitizers enabled.

[jamesmunns]

Hey @gnzlbg, that sounds like a good idea. If you have an idea of how to implement it, let me know! I think you might need to wait until #131 lands, since cross currently uses the host's Rust toolchain.

For now if your host system is using a version of std with sanitizer support, cros should use it.

[gnzlbg]

So one could compile std with sanitizer support using xargo, upload a docker image containing that, and expose it via cross API. Maybe as part of the target triple x86_64-unknown-linux-gnu-msan or as a flag in the config file.

[japaric]

So one could compile std with sanitizer support using xargo, upload a docker image containing that, and expose it via cross API.

if you put a std binary in the Docker image that std image will only work with a toolchain whose version is the exact same as the toolchain used to compile the std binary.

A more flexible solution that already works today is make Cross use Xargo to cross compile std with the sanitizer stuff enabled. You can set target.$TARGET.xargo to true in the Cross.toml and Cross should do that if the Docker image has a Xargo binary in it -- I think all Docker images do but haven't checked.

[Alexhuszagh]

This is now possible via cross rustc and -Zbuild-std:

$ cross +nightly rustc --target x86_64-unknown-linux-gnu -Zbuild-std -- -Zself-profile -Zsanitizer=leak

Currently, we should be able to support CARGO_TARGET_${TARGET}_RUSTFLAGS, however, we have another complicating issue in #903.