Avoid unsafePerformIO for getProgName
Avoid unsafePerformIO for getProgName
getProgName was used to append the name of the program (e.g. "ghc") to printed error messages in the Show instance of GhcException. It doesn't belong here as GHCi and GHC API users may want to override this behavior by setting a different error handler. So we now call it in the defaultErrorHandler instead.