Cycles and OpenGL draw tests need the idiff tool from
OpenImageIO, but install_deps.sh explicitly disables
This patch allows them to be built by default.
I would not enable that by default, this scripts is primarily intended to people who just want to build and use their own blender, not for the handful of devs that would actually run those tests. Please add it as an option of the script (ideally, a generic one like --enable-tests or something like that, that could be used in other places if/when needed, and that should also enable WITH_GTESTS and others in generated CMake config.
More space-on-disk used, longer compiling time? I don’t think that is anything critical here, but we are trying to only build bare minimal requirements here, we explicitly strip all that we don’t need, imho things required only for tests should be optional (as are gtests building in blender itself).