Update cmake flags

Author: serge-sans-paille

.github/workflows/llvm.yml

@@ -13,7 +13,7 @@ jobs:
           - windows-latest
           - macOS-latest
         cmake_args:
-          - ""
+          - "-DLLVM_ENABLE_PROJECTS='clang'"
     steps:
     - name: Setup Windows
       if: startsWith(matrix.os, 'windows')