Simplify build configuration

- Use ubuntu-24.04 runner so we get a more recent clang version
- Use native arm64 build, getting rid of zig
- Remove setup steps for dependencies that are already installed on the runner
  images
- Build using clang on Windows so we can use thinLTO there

Author: fhanau

.github/workflows/llvm.yml

@@ -18,7 +18,6 @@ env:
   LLVM_TARGETS: ${{ inputs.target }}
   LLVM_BINS: ${{ inputs.target }}
   LLVM_LIBS: ''
-  ZIG_VERSION: '0.16.0'
 jobs:
   create-release:
     runs-on: ubuntu-latest
@@ -42,22 +41,22 @@ jobs:
             STATIC_LIB_SUFFIX: 'a'
             LLVM_TARGETS_TO_BUILD: 'AArch64'
           - os: linux-amd64
-            runner: ubuntu-22.04
-            toolchain: clang-lld-linux-amd64
+            runner: ubuntu-24.04
+            toolchain: clang-lld-linux
             BIN_SUFFIX: ''
             SO_SUFFIX: 'so.${{ inputs.version }}'
             STATIC_LIB_SUFFIX: 'a'
             LLVM_TARGETS_TO_BUILD: 'X86'
           - os: linux-arm64
-            runner: ubuntu-22.04
-            toolchain: zig-linux-arm64
+            runner: ubuntu-24.04-arm
+            toolchain: clang-lld-linux
             BIN_SUFFIX: ''
             SO_SUFFIX: 'so.${{ inputs.version }}'
             STATIC_LIB_SUFFIX: 'a'
             LLVM_TARGETS_TO_BUILD: 'AArch64'
           - os: windows-amd64
             runner: windows-latest
-            toolchain: default
+            toolchain: clang-lld-windows
             # Exclude directories with links, which Windows can't handle
             TAR_ARGS: '--exclude=*/clang/test/Driver/Inputs/* --exclude=*/libcxx/test/std/input.output/filesystems/Inputs/static_test_env/* --exclude=*/libclc/amdgcn-mesa3d --exclude=*/llvm/utils/mlgo-utils/*'
             BIN_SUFFIX: '.exe'
@@ -68,29 +67,10 @@ jobs:
     name: ${{ matrix.platform.os }}
     steps:
       - uses: actions/checkout@v7
-      - name: Setup for macOS
-        if: runner.os == 'macOS'
-        run: |
-          brew install cmake ninja
-      - name: Setup for Linux
-        if: runner.os == 'Linux'
-        run: |
-          sudo apt-get install -y cmake ninja-build
       - name: Setup for Windows
         if: runner.os == 'Windows'
         run: |
-          choco install cmake ninja curl
-      - name: Get zig toolchain
-        if: startsWith(matrix.platform.toolchain, 'zig')
-        shell: bash
-        run: |
-            echo "zig is $ZIG_VERSION"
-            curl -L https://ziglang.org/download/${ZIG_VERSION}/zig-x86_64-linux-${ZIG_VERSION}.tar.xz -o zig.tar.xz
-
-            mkdir zig
-            tar -C zig --strip-components=1 -xJf zig.tar.xz
-            cd zig
-            pwd >> $GITHUB_PATH
+          choco install curl
       - name: Get llvm
         shell: bash
         run: |

build/llvm/clang-lld-linux-amd64.cmake build/llvm/clang-lld-linux.cmakebuild/llvm/clang-lld-linux-amd64.cmake renamed to build/llvm/clang-lld-linux.cmake

@@ -0,0 +1,8 @@
+# Toolchain file to build LLVM using clang-cl and link using lld-link.
+#
+set(CMAKE_C_COMPILER clang-cl)
+set(CMAKE_CXX_COMPILER clang-cl)
+
+# Tell LLVM's build system to link with lld (lld-link on Windows) instead of
+# the default MSVC linker. This is required for using thinLTO.
+set(LLVM_USE_LINKER lld CACHE STRING "" FORCE)