test cross compile on macos

.github/workflows/llgo.yml

@@ -200,13 +200,17 @@ jobs:
 
   cross-compile:
     continue-on-error: true
-    runs-on: macos-latest
+    strategy:
+      matrix:
+        os: [macos-latest]
+        llvm: [19]
+    runs-on: ${{matrix.os}}
     steps:
       - uses: actions/checkout@v4
       - name: Install dependencies
         uses: ./.github/actions/setup-deps
         with:
-          llvm-version: 19
+          llvm-version: ${{matrix.llvm}}
 
       - name: Set up Go for building llgo
         uses: ./.github/actions/setup-go