Add ghc-source-gen.
Add ghc-source-gen.

soenkehahn/stackage,spencerjanssen/stackage,fpco/stackage,Daniel-Diaz/stackage,asr/stackage,iand675/stackage,simonmichael/stackage,mrkkrp/stackage,fimad/stackage,massysett/stackage,clinty/stackage,michalkonecny/stackage,athanclark/stackage,jonschoning/stackage,stackbuilders/stackage,wereHamster/stackage