The compiler_builtins library is now a crates.io dependency of alloc

[phil-opp]

rust-lang/rust#56092 changed the build process of the sysroot in the following way:

The compiler_builtins is now a normal crates.io crate: https://crates.io/crates/compiler_builtins. Since compiler_buitlins depends on libcore, but no sysroot exists yet when building liballoc, it has a special rustc-std-workspace-core feature that overwrites the core dependency with an empty crates.io crate called rustc-std-workspace-core. This makes it possible to override the core dependency through a patch section in the Cargo.toml of liballoc.

For time reasons, this PR takes a different approach: Instead of using the rustc-std-workspace-core feature and a patch section to build core together with liballoc, we keep on building core first and then set the sysroot in RUSTFLAGS when compiling liballoc. This way, both liballoc and compiler_builtins use the core library that we built in the previous step.

Fixes #22

[phil-opp]

Published as 0.5.1

[HadrienG2]

Thanks for saving the uefi-rs build! 😃

[phil-opp]

You're welcome :)