ci: WIP actions build for LLVM on x86_64-unknown-linux-gnu

Author: tmarsteel

.github/workflows/build-llvm-linux.yaml

@@ -0,0 +1,70 @@
+# Copied from github.com/llvm/llvm-project Actions
+
+env:
+  LLVM_REF: llvmorg-20.1.8
+
+name: "Build LLVM for Linux"
+on:
+  workflow_dispatch:
+  workflow_call:
+
+jobs:
+  build-llvm-windows:
+    name: "Build LLVM x86_64-unknown-linux-gnu"
+    runs-on: ubuntu-22.04
+    env:
+      LLVM_INSTALL_PATH: ${{ github.workspace }}/llvm-install
+      LLVM_BUILD_PATH: ${{ github.workspace }}/llvm-build
+    steps:
+      - name: cache
+        id: cache
+        uses: actions/cache@v4.2.2
+        with:
+          path: |
+            ${{ env.LLVM_INSTALL_PATH }}
+          key: llvm-built-${{ env.LLVM_REF }}
+      - name: Fetch LLVM sources
+        if: steps.cache.outputs.cache-hit != 'true'
+        uses: actions/checkout@v4
+        with:
+          repository: llvm/llvm-project
+          ref: ${{ env.LLVM_REF }}
+          fetch-depth: 2
+      - name: install llvm-19
+        id: setup
+        run: sudo apt install clang-19
+      - name: Configure LLVM
+        if: steps.cache.outputs.cache-hit != 'true'
+        shell: bash
+        run: |
+          cmake \
+            -G "Ninja" \
+            -S llvm \
+            -B $LLVM_BUILD_PATH \
+            -DLLVM_BUILD_LLVM_C_DYLIB=ON \
+            -DLLVM_BUILD_LLVM_DYLIB=On \
+            -DLLVM_LINK_LLVM_DYLIB=On \
+            -DCMAKE_INSTALL_PREFIX=$LLVM_INSTALL_PATH \
+            -DCMAKE_BUILD_TYPE=Release \
+            -DLLVM_ENABLE_ASSERTIONS=On \
+            -DCMAKE_C_COMPILER=/usr/bin/clang-19
+            -DCMAKE_CXX_COMPILER=/usr/bin/clang-19
+            -DLLVM_TARGETS_TO_BUILD=X86 \
+            -DLLVM_ENABLE_DIA_SDK=OFF \
+            -DLLVM_ENABLE_LIBXML2=OFF \
+            -DLLVM_INCLUDE_TESTS=OFF \
+            -DPYTHON_EXECUTABLE="$(where python.exe | head -1)" \
+            -DLLVM_ENABLE_ZSTD=OFF \
+            -DLLVM_ENABLE_PROJECTS="llvm;lld"
+      - name: Build LLVM
+        if: steps.cache.outputs.cache-hit != 'true'
+        run: |
+          cd "${{ env.LLVM_BUILD_PATH }}"
+          ninja
+          ninja install
+      - name: Collect artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: llvm-linux-gnu-x86_64
+          path: |
+            ${{ env.LLVM_INSTALL_PATH }}