Respect prompt in GhciSettings
Respect prompt in GhciSettings

Summary:
This was broken when PromptFunction was introduced that the settings are
ignored and default values are always used.

Test Plan: ./validate

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc