gnome-extra/cinnamon-1.6.7-r2 looks for 'Meta-3.0.gir' in these search paths: ['.', '/usr/lib64/muffin', '/usr/local/share/gir-1.0', '/usr/share/gir-1.0', '/usr/share/gir-1.0', '/usr/share/gir-1.0', '/usr/share/gir-1.0'])

in an old locate database, i found that this file once was in /usr/lib64/muffin/Meta-3.0.gir

now it's no longer there, but there is Meta-Muffin.0.gir now (owned by muffin-1.8.2-r1).

I just created a dirty symlink: Meta-3.0.gir -> Meta-Muffin.0.gir

And now the build succeeds.