[$] Improving bindgen for the kernel

Bindgen is a widely used tool that automatically generates Rust bindings from C
headers. The

Rust-for-Linux project uses it to create some of
the bindings between Rust code and the rest of the kernel. John Baublitz
presented at Kangrejos about the improvements that he has made to the tool in
order to make the generated bindings easier to use, including improved support
for macros, bitfields, and enums.