[Java] Use CC and CXX ENV variables

Author: vyazelenko

.github/workflows/ci.yml

@@ -79,7 +79,8 @@ jobs:
  matrix:
  gcc: [ 6, 7, 8, 9 ]
  env:
- COMPILER: g++-${{ matrix.gcc }}
+ CC: gcc-${{ matrix.gcc }}
+ CXX: g++-${{ matrix.gcc }}
  steps:
  - name: Checkout code
  uses: actions/checkout@v2