use clang as the brew compiler

Author: perazz

.github/workflows/meta.yml

@@ -198,7 +198,7 @@ jobs:
     - name: (macOS) Install homebrew OpenMPI
       if: contains(matrix.mpi,'openmpi') && contains(matrix.os,'macos')
       run: |
-        brew install --cc=gcc-${{ env.GCC_V }} openmpi
+        brew install openmpi #--cc=gcc-${{ env.GCC_V }} openmpi
 
     # Phase 1: Bootstrap fpm with existing version
     - name: Install fpm