[$] Improving bindgen for the kernel

Bindgen is a widely used tool that automatically generates Rust bindings from Cheaders. TheRust-for-Linux project uses it to create some ofthe bindings between Rust code and the rest of the kernel. John Baublitzpresented at Kangrejos about the improvements that he has made to the tool inorder to make the generated bindings easier to use, including improved supportfor macros, bitfields, and enums.