Fix the failures on Crater

[tomassedovic]

Crater is a tool that compiles everything on http://crates.io with two version of the Rust compiler to detect breakage.

Tcod is failing, because the build script in tcod-sys is expecting SDL stuff that's not present in the build environment:

https://tools.taskcluster.net/task-inspector/#oHQxc8A-REGyGXfzk37EPQ/
https://tools.taskcluster.net/task-inspector/#KXt0JaJ9QXWWBJsMyttAFg/

See the last few comments on #205 for some discussion around this. Since we only care about the Rust code for Crater runs, we can use its environment variables to detect that and not do anything in build.rs.

[zsparal]

I was under the impression that SDL is a hard dependency for libtcod (at least the makefiles don't seem to indicate otherwise). I might be misunderstanding how cargo build works, but doesn't tcod-rs need tcod_sys which in turn depends on SDL to be present?

[tomassedovic]

Yes if you actually want to use it. But I think you can still compile the rust code without it.

But I'm thinking, we don't build libtcod at all, basically making build.rs a no-op. So when you actually try to run any of the samples or whatever, you'd get a linker failure. But tcod and tcod-sys should still compile I think -- which is all we care about with crater.

[zsparal]

You're right. For some reason I thought tcod_sys would fail, but I guess I was wrong.

[tomassedovic]

Well we still need to verify this, I'm just guessing here. But I think it should work.

[zsparal]

I just tried it with build.rs completely commented out. build works just fine, test or run --example fails with linker errors, just as you said.

[tomassedovic]

\o/