Unstable features and macros tracking issues

[orangecms]

Same as they are doing in Rust for Linux: Rust-for-Linux/linux#2

Remarks

We cannot use a stable version as of now because we're using some -Z flags; this would be printed:

RUST_TARGET_PATH=/home/user/oreboot/src/custom_targets cargo build --target "x86_64-unknown-none-oreboot" -Z build-std=core,alloc --verbose --release
error: the `-Z` flag is only accepted on the nightly channel of Cargo, but this is the `stable` channel

Howto

Look at the stable release of the Rust unstable book to find the references and compare with the nightly release of the book.

Here's a list of unstable things we're using (TODO: complete the list!)

Compiler Features

• build-std
• emit-stack-sizes

Language Features

• asm_const
• document use of naked_functions #629
• default_alloc_error_handler

[bwerthmann]

I spiked on this for just the nezha as far as I could get with make RUSTUP_TOOLCHAIN=1.66. See branch https://github.com/bwerthmann/oreboot/tree/551-unstable-features-and-macros-tracking-issues for patches. I only compile tested this code.

I ran out of runway here:

   Compiling oreboot-nezha-bt0 v0.1.0 (/home/ben/ofw/oreboot/src/mainboard/sunxi/nezha/bt0)
error[E0554]: `#![feature]` may not be used on the stable release channel
 --> src/mainboard/sunxi/nezha/bt0/src/main.rs:2:1
  |
2 | #![feature(naked_functions, asm_const)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0554]: `#![feature]` may not be used on the stable release channel
 --> src/mainboard/sunxi/nezha/bt0/src/main.rs:3:1
  |
3 | #![feature(default_alloc_error_handler)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^