Enable Rust in the Linux kernel

Description:

Enable Rust in the kernel build for rust modules support.

Here i attached some possible changes to the config and PKGBUILD files.

This will add rustc and llvm as a makedepend.

Additional info:

• package version(s): 6.9.7.arch1-1
• it requires the rust toolchain version 1.76 as of kernel 6.9

  • it is setup automatically by running

    rustup override set $(scripts/min-tool-version.sh rustc)

    rustup component add rust-src

    cargo install --locked --version $(scripts/min-tool-version.sh bindgen) bindgen-cli

• When building, pass LLVM=1 to the make command.
• config file
  • just enable rust from nconfig
• PKGBUILD example
  • from my limited testing if make htdocs is enabled the build freezes, as of now i don't know why ("WARNING: Duplicate C declaration") but after a while it starts back. As of now i have no idea of why id does that, it must be fixed.
• Linux kernel documentation for Rust

Steps to reproduce:

1. Build the kernel with the default PKGBUILD
2. Try to load a kernel module written in Rust
3. It fails to load