Gtk3 and gdk-pixbuf2 for cos7

[hmaarrfk]

These would be useful for better desktop integration for Qt5 (and Qt6 eventually)

see discussion conda-forge/qt-main-feedstock#98 (comment)
Checklist:

• Revert iteritems fix Do not use removed iteritems from conda_build #62

• if you have added a CDT, it appears in the cdt_slugs.yaml file and
  you have rerun the script python gen_cdt_recipes.py.

• if you have changed the CDT generator code (rpm.py), you have bumped
  the build number in conda_build_config.yaml and have remade all of the
  recipes via running python gen_cdt_recipes.py --force

• if you have added a custom CDT recipe, you have added the name of the CDT
  with custom: true in the cdt_slugs.yaml file.

• all CDT recipes have build number set by {{ cdt_build_number }} for
  old-style/legacy CDTs or {{ cdt_build_number|int + 1000 }} for new-style CDTs

• if you see a warning about a CDT not having a license, you have added the
  license_file key in the cdt_slugs.yaml file with the path to the appropriate
  license in licenses/

NOTE: If you make any changes to cd_slugs.yaml, you need to reun the generator code
via python gen_cdt_recipes.py.

[isuruf]

Using a CDT is equivalent to the following steps

1. Building using an old version of the library
2. Removing the run requirement of the library by ignoring the run_exports

Can this not be done for GTK3 which has a conda package?

[hmaarrfk]

i am in the process of building these locally to tes this out. I'll set this as a draft until I can confirm.

[hmaarrfk]

Can the approach of using the CDTs for Qt be discussed conda-forge/qt-main-feedstock#98 (comment)