converters/wkhtmltopdf: Fix build with gcc10
The patch is accepted from Debian:
https://salsa.debian.org/qt-kde-team/qt/qt4-x11/commit/0d4a3dd61ccb156dee556c214dbe91c04d44a717
Still keep it DEPRECATED and see how it builds on 13.X series.
PR: 269313
Reported by: r.quakkelaar@quaras.nl
Approved by: portmgr (just-fix-it)