Disk space and LTO improvements in Rustc and Cargo

I’m excited by these changes. Rust compilation times, although slow, have been improving by 20-40% every year. The changes in the linked post alone improve LTO build times by 4-20%.

I’m also looking forward to other changes that people have been working on.

- A debug backend that uses Cranelift instead of LLVM improves debug compile times by 20-50%.

- Using pre-compiled release binaries for procedural macros. Today this causes a major hit to compile times because the macro needs to be compiled, then do some codegen, and then the compilation of actual code + generated code proceeds.

- In the long term (probably years), the compiler is able to run interactively, recompiling when any changes are made.