Fix windows flags

Author: LucasSte

.github/workflows/premerge.yaml

@@ -119,6 +119,9 @@ jobs:
           echo "windows-check-targets=${windows_check_targets}" >> $GITHUB_OUTPUT
       - name: Build and Test
         if: ${{ steps.vars.outputs.windows-projects != '' }}
+        env:
+          CC: 'clang'
+          CXX: 'clang++'
         shell: cmd
         run: |
           set MAX_PARALLEL_COMPILE_JOBS=64