How do I tell hadrian/build which GHC to build hadrian with?

For context: I encountered this issue while bisecting #21994.

hadrian/build[-cabal] apparently doesn't use the stage0 compiler chosen via ./configure to build hadrian itself. Is there a better way to select this GHC version than by modifying the executable PATH?

I was expecting to find this information at https://gitlab.haskell.org/ghc/ghc/-/wikis/building/hadrian or https://gitlab.haskell.org/ghc/ghc/blob/master/hadrian/README.md but I did not.

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