GHC flags taken into account too late

[nomeata]

It seems that

hs-to-coq --ghc -package-env=hs-to-coq.env

doesn’t work the way it should, but

GHC_ENVIRONMENT=hs-to-coq.env hs-to-coq

does.

Some wild guess: We need to extract the --ghc flags and pass them to the GHC API earlier, maybe in lib/HsToCoq/Util/GHC.hs.

(Not working on that right now, the work-around is fine for now.)