Add support for building CIRCT from source

[jerryz123]

Unfortunately, some machines we use cannot run the CIRCT nightlies, with no workaround besides building CIRCT from source.
This adds a script and flag to build-setup to build CIRCT from source.

Related PRs / Issues:

Type of change:

• Bug fix
• New feature
• Other enhancement

Impact:

• RTL change
• Software change (RISC-V software)
• Build system change
• Other

Contributor Checklist:

• Did you set main as the base branch?
• Is this PR's title suitable for inclusion in the changelog and have you added a changelog:<topic> label?
• Did you state the type-of-change/impact?
• Did you delete any extraneous prints/debugging code?
• Did you mark the PR with a changelog: label?
• (If applicable) Did you update the conda .conda-lock.yml file if you updated the conda requirements file?
• (If applicable) Did you add documentation for the feature?
• (If applicable) Did you add a test demonstrating the PR?

• (If applicable) Did you mark the PR as Please Backport?

[joonho3020]

LGTM

[abejgonzalez]

I think it would be a good idea to change our full flow CI (which is used for CAD stuff + other) to use this flag (just to cover that the build works).

[jerryz123]

I think it would be a good idea to change our full flow CI (which is used for CAD stuff + other) to use this flag (just to cover that the build works).

This does massively blow up the run time of that flow though.... I'm actually ok with not testing this in CI... its for one very specific environment. Very few people should use this.

[seldridge]

Drive by comments/ideas: Any caching can speed up the builds. This can either be "cache the whole CIRCT build result" or using ccache/sccache on top of a build and preserving the ccache/sccache across builds. The latter is usually easier to deal with and does have benefits of allowing caching across similar, but not identical builds.