Upon upgrading with `guix upgrade`, ghc-8.6.5 is downloaded, but the build phase seems to get stuck at 100%.
- bug#36972: ghc-8.6.5 won't complete its build phase Brian Leung
- bug#36972: ghc-8.6.5 won't complete its build phase Timothy Sample
- bug#36972: ghc-8.6.5 won't complete its build phas... Timothy Sample
