Improve `config_fast_builds.toml`

[BD103]

Objective

• config_fast_builds.toml could use some general improvements and additions.
  • Mold is a modern linker with serious performance improvements that provides a good alternative to LLD.

Solution

• Majorly improve config_fast_builds.toml.
  • Add further documentation.
  • Add a section for the alternative Mold / Sold linker, which is much faster.
  • Disable nightly options by default so that developers running stable can copy the file without having to edit it. (Nightly is still recommended, but this is following suite with rustfmt.toml.)

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Changelog

• Majorly improved config_fast_builds.toml documentation and added Mold / Sold linker.

[BD103]

Initial tests in CI appears to speed up the MacOS build times by ~2 minutes, but slows down Linux by ~45 seconds and Windows by ~2 minutes. I think this is due to apt-get update and cargo install -f cargo-binutils.

I'm going to look into downloading a prebuit cargo-binutils, and seeing if there is a better way to install LLD on Linux.

[BD103]

I'm going to split out the CI code into a separate PR so this can be merged.

[mockersf]

sold is pretty much abandoned at this point, is it even worth it to mention it?

Actually, even llvm... apple released a new faster linker, which is why sold was abandoned

[BD103]

sold is pretty much abandoned at this point, is it even worth it to mention it?

Actually, even llvm... apple released a new faster linker, which is why sold was abandoned

That's a good point. I think I'll remove references to Sold and add a comment to the MacOS tables saying that the builtin ld64 may provide better performance than LLD.