ghc8: apply patches to fix https://ghc.haskell.org/trac/ghc/ticket/12130

Namely:

https://git.haskell.org/ghc.git/commitdiff/4d71cc89b4e9648f3fbb29c8fcd25d725616e265
https://git.haskell.org/ghc.git/commitdiff/2f8cd14fe909a377b3e084a4f2ded83a0e6d44dd