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)