Simplify kernel build recipe

Move a bunch of options from recipe.toml to Cargo.toml and the target specs. Also make rustc invoke the linker rather than having the recipe run it. And finally switch the linker to the lld bundled with rustc.

mentioned in merge request cookbook!301 (merged)

mentioned in merge request !254 (merged)

merged

Those changes seem to break the global build make all. I get the following error:

error: no library targets found in package `kernel`

Adding the lib section back solved the issue:

[lib]
name = "kernel"
path = "src/main.rs"
crate-type = ["staticlib"]

Did you update the cookbook? cookbook!301 (merged) has the associated cookbook changes to build the kernel as bin instead of as staticlib.

Indeed, for some reason I was on 6d513c49 instead of master (02b814dc).