added test for upstream clang on macos-14, as an example for an arm64 platform

.github/workflows/ci-test-package-cmake.yml

@@ -136,6 +136,20 @@ jobs:
               cxx_modules: "False",
               std_format_support: "True"
             }
+          - {
+              name: "Clang-18 on Apple M1 (arm64)",
+              os: macos-14,
+              compiler:
+                {
+                  type: CLANG,
+                  version: 18,
+                  cc: "/opt/homebrew/opt/llvm@18/bin/clang-18",
+                  cxx: "/opt/homebrew/opt/llvm@18/bin/clang++",
+                },
+              lib: "libc++",
+              cxx_modules: "False",
+              std_format_support: "True"
+            }
           - {
               name: "Apple Clang 15",
               os: macos-14,
@@ -188,8 +202,8 @@ jobs:
         shell: bash
         run: |
           sudo apt install -y g++-${{ matrix.config.compiler.version }}
-      - name: Install Clang
+      - name: Install Clang with apt
-        if: matrix.config.compiler.type == 'CLANG'
+        if: matrix.config.compiler.type == 'CLANG' && matrix.config.os != 'macos-14'
         shell: bash
         working-directory: ${{ env.HOME }}
         run: |
@@ -197,8 +211,13 @@ jobs:
           chmod +x llvm.sh
           sudo ./llvm.sh ${{ matrix.config.compiler.version }}
           sudo apt install -y clang-tools-${{ matrix.config.compiler.version }}
+      - name: Install Clang using homebrew
+        if: matrix.config.compiler.type == 'CLANG' && matrix.config.os == 'macos-14'
+        shell: bash
+        run: |
+          brew install llvm@18
       - name: Install Libc++
-        if: matrix.config.compiler.type == 'CLANG' && matrix.config.lib == 'libc++'
+        if: matrix.config.compiler.type == 'CLANG' && matrix.config.lib == 'libc++' && matrix.config.os != 'macos-14'
         shell: bash
         run: |
           sudo apt install -y libc++-${{ matrix.config.compiler.version }}-dev libc++abi-${{ matrix.config.compiler.version }}-dev libunwind-${{ matrix.config.compiler.version }}-dev