hadrian: enable terminfo if --with-curses-* flags are given

The GHC make build system used to support WITH_TERMINFO in ghc.mk which allowed controlling whether to build GHC with terminfo or not. hadrian has replaced this with a system where this is effectively controlled by the cross-compiling setting (the default WITH_TERMINFO value was bassed on CrossCompiling, iirc).

This behavior is undesireable in some cases and there is not really a good way to work around it. Especially for downstream packagers, modifying this via UserSettings is not really feasible since such a source file has to be kept in sync with Settings/Default.hs manually since it can't import Settings.Default or any predefined Flavour definitions.

To avoid having to add a new setting to cfg/system.config and/or a new configure flag (though I'm happy to implement both if required), I've chosen to take --with-curses-* being set explicitly as an indication that the user wants to have terminfo enabled.

Please let me know if this change requires an entry to the release notes.