Attempt to install clang in musl builds

.github/workflows/build_cibuildwheel.yml

@@ -28,8 +28,8 @@ jobs:
           CIBW_ARCHS: auto64
           CIBW_ARCHS_MACOS: universal2
           CIBW_ENVIRONMENT_MACOS: MACOSX_DEPLOYMENT_TARGET=10.15
-#          CIBW_ENVIRONMENT_LINUX: CXX=clang++
-          CIBW_SKIP: "*musllinux*"
+          CIBW_BEFORE_BUILD_LINUX: apk add clang | echo "ok"
+          CIBW_ENVIRONMENT_LINUX: CXX=clang++
 
       - uses: actions/upload-artifact@v2
         with: