[DO NOT MERGE YET] Bump clone-llvm.sh to ROCm/llvm-project, retire mlirDistroRocm.yml

[jgmelber]

Summary

Follow-up to #3324 (repoints mlirDistro.yml at ROCm/llvm-project, not yet merged). This is the second stage of the migration: it flips every downstream consumer over to the ROCm-built MLIR by bumping the shared version pin.

• utils/clone-llvm.sh: bumped LLVM_PROJECT_COMMIT/DATETIME to the commit already validated end-to-end in [TEST] Add ROCm migration test workflow #3314 (46fcb339, ROCm/llvm-project) — this is the single file every downstream consumer (mlirAIEDistro.yml, buildAndTestPythons.yml, buildAndTestMulti.yml, buildAndTestVitis.yml, buildAndTestAieTools.yml, buildAndTestAieToolsHsaBuildOnly.yml, buildAndTestRyzenAISw.yml, buildRyzenWheels.yml, lintAndFormat.yml, generateDocs.yml, buildAndTestRyzenAI.yml) reads via --get-wheel-version to know which mlir wheel version to pip install from the mlir-distro release tag.
• .github/workflows/mlirDistroRocm.yml deleted — retired now that mlirDistro.yml (via Repoint mlirDistro.yml at ROCm/llvm-project #3324) builds from ROCm directly, making the standalone pipeline redundant.
• .github/workflows/update-llvm.yml: paused the biweekly automatic schedule (kept workflow_dispatch). utils/update_llvm_version.py is hardcoded to llvm/llvm-project (and cross-checks torch-mlir/eudsl compatibility windows that don't apply to the ROCm fork) — left running, it would silently open PRs proposing to revert this migration within ~2 weeks. Making the updater ROCm-fork-aware and re-enabling the schedule is tracked in Make update-llvm.yml ROCm-fork-aware (re-enable auto LLVM updates post-migration) #3336.

DO NOT MERGE until

1. Repoint mlirDistro.yml at ROCm/llvm-project #3324 is merged, and mlirDistro.yml has been manually dispatched with LLVM_COMMIT=46fcb339fb61119b337f973c7ca9e710a319fdd0 pinned explicitly (not auto-latest), so the mlir-distro release actually has a published wheel matching 23.0.0.2026071017+46fcb339. Skipping this step is exactly what broke Repoint mlirDistro.yml at ROCm/llvm-project #3324 when this was all one PR — every consumer 404s immediately if the version this PR pins to doesn't already exist under mlir-distro.
2. [TEST] ROCm mlir_aie wheel on Ryzen AI self-hosted runners #3323 (validate the ROCm-built wheel on Ryzen AI self-hosted runners) has run and passed.

Opened as a draft for that reason — flip to ready-for-review once both gates above are satisfied.

Test plan

• Repoint mlirDistro.yml at ROCm/llvm-project #3324 merged and mlir-distro confirmed to have a 23.0.0.2026071017+46fcb339 wheel
• [TEST] ROCm mlir_aie wheel on Ryzen AI self-hosted runners #3323 passing on both aie2-4col and aie2p-8col
• Re-run this PR's own CI (buildAndTestPythons, mlirAIEDistro, etc.) and confirm they now resolve/install the ROCm-built wheel successfully

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