Created attachment 474522 [details] Build Log ebuilds which call haskell-cabal_src_compile() try to compile with the flag -nopie, which is undefined in gcc-6.3.0 and should be -no-pie instead. I've linked the build log of dev-haskell/http-client as an example.
Created attachment 474524 [details] System Info
Fixed by running haskell-updater; this is working as intended.