Nix gtk2+ package not recognized during openjfx build

So I’m trying to build OpenJFX11 following this guide. When I try to build the SDK with gradle sdk I get this error:

FAILURE: Build failed with an exception.
* Where:
Script '/home/skykanin/Documents/rt-2bc030c56a59/buildSrc/linux.gradle' line: 105
* What went wrong: A problem occurred evaluating script.
> GTK2 development packages not found. If GTK2 packages are installed, please remove the build directory and try again.

So I tried to use a nix-shell environment to make sure gtk2 was available like so:
nix-shell -p binutils ant gnome2.gtk but when I tried to build the SDK again it still failed with the same error. I also tried using gtk2-x11 instead, but that didn’t work either.

nix-shell is certainly the right approach. You may need to add pkgconfig to the list of packages as well, since that’s often used to find dependencies.