ghc-8.12

synopsis: Support GHC-8.12
prs:
  #6735 #6844 #6865 #6848 #6908 #6947
  #6552 #6553 #6563 #6545
issues: #6903 #6904 #6905
significance: significant

description: {

- Support for `-this-package-key` deprecation
- Use process `createPipe`
- Add support for WINIO to Cabal
- Adopt to simplfied subsumption changes

There are no magical `IO = WithCallStack Prelude.IO` alias in Cabal,
as it is hard to get working with GHC-8.12's simplified subsumption.

}