Install Clang

Copied from the JIT workflow

Author: zanieb

.github/workflows/reusable-ubuntu.yml

@@ -76,6 +76,14 @@ jobs:
       with:
         path: ${{ env.CPYTHON_BUILDDIR }}/config.cache
         key: ${{ github.job }}-${{ runner.os }}-${{ env.IMAGE_VERSION }}-${{ inputs.config_hash }}
+    - name: Install Clang
+      if: ${{ fromJSON(inputs.bolt-optimizations) }}
+      run: |
+        sudo apt-get update
+        sudo apt-get install ca-certificates
+        sudo update-ca-certificates
+        sudo bash -c "$(wget -O - https://apt.llvm.org/llvm.sh)" ./llvm.sh 19
+        echo PATH="$(llvm-config-19 --bindir):$PATH" >> $GITHUB_ENV
     - name: Configure CPython out-of-tree
       working-directory: ${{ env.CPYTHON_BUILDDIR }}
       run: >-