Use lld when building with mzcompose on macOS

[def-]

$ bin/mzcompose --find testdrive down && bin/mzcompose --find testdrive --dev run default
$ echo >> src/materialized/src/bin/materialized.rs
$ bin/mzcompose --find testdrive down && bin/mzcompose --find testdrive --dev run default
[...]
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 7.35s

Before this PR:

$ bin/mzcompose --find testdrive down && bin/mzcompose --find testdrive --dev run default
$ echo >> src/materialized/src/bin/materialized.rs
$ bin/mzcompose --find testdrive down && bin/mzcompose --find testdrive --dev run default
[...]
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 6m 35s

@teskje Can you try if this works for you?

Independently of this, we should also bump the crosstools-ng and the software it pulls it to get parity with ci-builder: MaterializeInc/homebrew-crosstools#10

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.

[benesch]

This makes a ton of sense. Just one comment about limiting the -B argument to just lld.

@def- I'm inclined to say that if we go this route, we shouldn't have the homebrew-toolchains repo try to install lld into this sysroot. In theory the homebrew-toolchains are meant to be usable by folks outside Materialize and those folks might not want to be forced to install lld. And using lld downstream, as demonstrated here, looks pretty clean!

[def-]

I'm inclined to say that if we go this route, we shouldn't have the homebrew-toolchains repo try to install lld into this sysroot.

Yes, absolutely. I'm not able to get that PR working properly though, and probably less importance.

[benesch]

LGTM!

[teskje]

Works like a charm!