panic! (the 'impossible' happened) with gi-gtk 3.0.4

I'm able to get two different panics, depending on how I try to build gi-gtk.

Firstly, on my mac:

brew install gtk+3
stack unpack gi-gtk-3.0.4
cd gi-gtk-3.0.4
stack init --resolver nightly-2016-06-08
PKG_CONFIG_PATH=/usr/local/opt/libffi/lib/pkgconfig/ stack build

This results in

[650 of 650] Compiling GI.Gtk           ( GI/Gtk.hs, .stack-work/dist/x86_64-osx/Cabal-1.24.0.0/build/GI/Gtk.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 8.0.1 for x86_64-apple-darwin):
        RnEnv.plusAvail bindingSignalWriteNext CheckButtonK{CheckButtonK}

Secondly, also on my mac, but within an ubuntu-based docker image:

docker run -it snoyberg/stackage:nightly
cd ~
stack unpack gi-gtk-3.0.4
cd gi-gtk-3.0.4
stack init --resolver nightly-2016-06-08
stack build

This results in

[599 of 654] Compiling GI.Gtk.Objects.Widget ( GI/Gtk/Objects/Widget.hs, .stack-work/dist/x86_64-linux/Cabal-1.24.0.0/build/GI/Gtk/Objects/Widget.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 8.0.1 for x86_64-unknown-linux):
        urk! lookup local fingerprint
  $fAttrInfoWidgetMarginTopPropertyInfo4

The latter panic was first observed on the stackage build server, during the June 8th nightly build. That's why, to use the same dependencies, I specified the nightly-2016-06-08 stack resolver in order to reproduce it. I originally recorded it here: https://github.com/fpco/stackage/issues/1569

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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