Hello,

I ended up disabling tests (see comments in the patch).
Now the package builds, but tries to install into the Qt directory; at the
end of the cmake phase, it prints:
  -- Installing in the same prefix as Qt, adopting their path scheme.
The previous version of the package contains a phase to adapt this,
but the .pri files to be modified do not exist any more.

I also tried to inherit from qtsvg like other qt* packages; but the
gnu-build-system does not work any more for qtwebkit, the build finishes
in a few seconds creating only the documentation and not compiling the code...

At this point, I am giving up; it would be nice if someone else could take
a look, I am attaching the current patch.

If there is no progress during the next few days, I would suggest to re-add
pyqt@5.9 for calibre. What do you think?

Andreas

PS: There is a thread from 2016 in which the Calibre author states that he
    will stick with qtwebkit and in the worst case take over the maintenance
    of a fork:
       https://www.mobileread.com/forums/showthread.php?t=270258