make without warnings

[philderbeast]

Seen with up-do/dex-lang@062c46a, there's a bunch of warnings. Can we make without warnings please?

$ make -f project-files.mk
updo/project-dhall/Makefile:59: warning: overriding recipe for target 'ghc-8.10.7.dhall2stack.yaml'
updo/project-dhall/Makefile:52: warning: ignoring old recipe for target 'ghc-8.10.7.dhall2stack.yaml'
updo/project-dhall/Makefile:73: warning: overriding recipe for target 'ghc-8.10.7.dhall2cabal.project'
updo/project-dhall/Makefile:66: warning: ignoring old recipe for target 'ghc-8.10.7.dhall2cabal.project'
updo/project-dhall2config/Makefile:75: warning: overriding recipe for target 'ghc-8.10.7.dhall2config.project'
updo/project-dhall2config/Makefile:64: warning: ignoring old recipe for target 'ghc-8.10.7.dhall2config.project'
stack build --test --no-run-tests --bench --no-run-benchmarks --dry-run --stack-yaml stack.yaml
...