[Test] Add CXX and CC configuration

.github/workflows/build.yml

@@ -72,6 +72,8 @@ jobs:
         # and build directories, but this is only available with CMake 3.13 and higher.  
         # The CMake binaries on the Github Actions machines are (as of this writing) 3.12
         run: |
+          export CC = ${{ matrix.config.cc }}
+          export CXX = ${{ matrix.config.cxx }}
           cmake $GITHUB_WORKSPACE -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DCMAKE_C_COMPILER_LAUNCHER=ccache -DCMAKE_CXX_COMPILER_LAUNCHER=ccache
 
       - name: Build