Update for rustc

This first commit fixes the ICE, but I've got another problem behind:

```
src/gl/lib.rs:88:1: 96:2 error: expected ident, found `$`
src/gl/lib.rs:88 generate_gl_bindings! {
src/gl/lib.rs:89     api: "gl",
src/gl/lib.rs:90     profile: "core",
src/gl/lib.rs:91     version: "4.5",
src/gl/lib.rs:92     generator: "global",
src/gl/lib.rs:93     extensions: [
```