Make the documentation build work on CloudABI.
Make the documentation build work on CloudABI.

Just like with wasm, we can't just import unix::ext and windows::ext.
Our shims are not complete enough for that.

GBGamer/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust