Comment 5 for bug 1317116

Same problem with gtk3:

$ sudo apt install libgtk-3-dev:amd64 libgtk-3-dev:i386
Reading package lists... Done
Building dependency tree
Reading state information... Done
libgtk-3-dev is already the newest version (3.22.28-1ubuntu3).
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 libgtk-3-dev:i386 : Depends: libgdk-pixbuf2.0-dev:i386 (>= 2.30.0) but it is not going to be installed
                     Depends: libpango1.0-dev:i386 (>= 1.40.5) but it is not going to be installed
                     Depends: libegl1-mesa-dev:i386 but it is not going to be installed
                     Depends: libxkbcommon-dev:i386 but it is not going to be installed
E: Unable to correct problems, you have held broken packages.