Refactor options fields to use PerCompilerFlavor type

[phadej]

E.g. jaeger-flamegraph.cabal failed to roundtrip 'pretty . parse';

Making the list business work didn't feel right,
so I made a bit bigger refactor.

Summary of the patch:

- options :: [(CompilerFlavor,[String])]
+ options :: PerCompilerFlavor [String]

where

-- | 'PerCompilerFlavor' carries only info per GHC and GHCJS
-- Cabal parses only @ghc-options@ and @ghcjs-options@, others are omitted.
data PerCompilerFlavor v

---

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[phadej]

Does appveyor fails because I changed GPD and tests assume cabal-install used to build project uses the same format as Cabal under test provides (i.e. caches). This is bizarre if it's that way.

[phadej]

With this patch hackage-tests roundtrip passes. (we don't run it in the CI as it takes 5+ minutes)