There are a few motivations for this change:
1. lld is demonstrably faster than gold, but is really only stable on
Linux at the moment. There's a good chance that it will be ready for
all platforms soon though.
2. Most people do not have gold installed on MacOS and Windows. You'd
have to do this manually through homebrew. I think it's a safe
assumption that this probably won't be slowing things down much on
those platforms.
3. We need to remove all configuration of the build that happens while
running `./mach build` if we ever hope to make `cargo build`
equivalent to the mach build. This unlocks static configuration of
the rustflags. One of the big blockers for proper `cargo build`
support.
This change makes rustup a requirement for building Servo with `./mach`
and switches to the newer `rust-toolchain.toml` format. The goal here is
to make mach builds more similar to non-mach builds.
- The new format allows listing the required components, removing some of
the complexity from our mach scripts.
- This means we must raise the required version of rustup to 1.23. The
current version is 1.26.
- We no longer wrap every call to cargo and rustc in "rustup run" calls
as both cargo and rustc will take care of installing and using all
necessary components specified in `rust-toolchain.toml` when run
inside the project directory.
Currently, ld.gold is always used for linking if found on the
system. There are some cases however when one may want to opt out
from using it. This patch adds the boolean field `rustc-with-gold`
to the `[tools]` section of `.servobuild`, which if set false,
disables the use of ld.gold.
This avoids changing any directories outside the repo, which is better for
some automation scenarios.
The servobuild.example file has a "cache-dir" setting that restores the
previous default location of `~/.servo`, which is useful for developers
working with multiple clones on the same machine.
