Updating spice-gtk blocked for the last four months

[Ralph Seichter]

Please see https://trac.macports.org/ticket/62212

I'd be thankful if a kind sould could resolve this issue which has
prevented me from updating spice-gtk for four months now, which in turn
is preventing updating the virt-manager port. I don't have enough
insight in the build process intricacies to fix it myself. Thank you.

-Ralph