Build settings with make/Hadrian rather than configure

This blocks to !655 (merged), which is the first step towards #16503 (closed).

To be clear it's unclear whether this is actually needed to get rid of Config.hs and just use settings, but given that Config.hs references paths built by make, I think this is the more natural way to do things ensuring that the proper dependencies exist. Put another, I think 1) get rid of compile-time configuration state (i.e. settings is runtime wrt to the GHC that uses it.) 2) once the configuration state is reduced, figure out how things really ought to work.

I'm mainly opening this separately from !655 (merged) so as to get some CI results that what's done so far works. It makes perfect sense to just merge !655 (merged) containing this as only then will settings be depending on make/Hadrian-only state.

CC @angerman @bgamari

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