#[start] makes --test not work

[brson]

I don't know what the failure mode is but I have heard that --test does not work if you define #[start].

[alexcrichton]

src/librustc/front/test.rs strips functions with the main attribute and injects its own, so I suppose this could be fixed by also stripping functions with the #[start] attribute

[alexcrichton]

Closing as a dupe of #8464 (that one has a bit more info)