Enable --include-iree-libs fetch and -DTHEROCK_ENABLE_IREE_LIBS build by default

[ScottTodd]

Motivation

Multi-arch CI is now enabled by default in TheRock, so we should make the default for developers match what CI is doing.

See:

• [Multi-arch] Enable multi-arch CI on pre-submit #3337
• [Plugin] Enable fusilli plugin build in TheRock iree-org/fusilli#57
• Build + test fusilliprovider in rocm-libraries CI rocm-libraries#6903

Technical Details

• This will add 45s+ to initial clone time when using the legacy fetch options.
  • Repositories that have not yet migrated to the --stage mode of fetching sources will pay this extra cost if they don't explicitly opt-out of the new setting.
• This will enable a few new subproject builds (IREE's LLVM, fusilli, etc.) by default which are already enabled for multi-arch CI.
  • Repositories that have not yet migrated to multi-arch CI may want to opt-out with -DTHEROCK_ENABLE_ALL=OFF -DTHEROCK_ENABLE_*=ON for some subset (as rocm-libraries already does) or -DTHEROCK_ENABLE_IREE_LIBS=OFF
  • The iree-compiler artifact is still annotated with disable_platforms = ["windows"] in BUILD_TOPOLOGY.toml, so the builds remain disabled there

Test Plan

• Multi-arch CI on this PR
• Non-multi-arch CI on this PR (watch fetch time and build time, see how non-multi-arch CI in other repositories may want to adapt)
  • https://github.com/ROCm/TheRock/actions/runs/25464273855?pr=5093
  • https://therock-ci-artifacts-external.s3.amazonaws.com/ROCm-TheRock/25464273855-linux/logs/gfx94X-dcgpu/index.html
  • https://therock-ci-artifacts-external.s3.amazonaws.com/ROCm-TheRock/25464273855-linux/logs/gfx94X-dcgpu/iree-compiler_build.log (~5 minutes to build iree-compiler)

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.

[marbre]

Yeah, another LLVM copy by default ;)

[ScottTodd]

cc a few people from the discussion on ROCm/rocm-libraries#6903: @jayhawk-commits @BrianHarrisonAMD @geomin12 (review if you'd like)