This patch was a bit on the harder side. We already have the
cairo->poppler->cairo cyclical dependency, so both cairos need to be
patched, the one in gtk.scm and the custom cairo in poppler. Also made
sure to grab cairo-xcb in the process.

cairo-xcb needs 'replacement #f' or else 'guix build cairo-xcb' returns
cairo, and I threw it in for the custom cairo in poppler after assuming
it would give a similar problem.

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Efraim Flashner   <efraim@flashner.co.il>   אפרים פלשנר
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