compilation of x11/qt5-qtwebkit on pkgsrc-2020Q4 branch

[Aymeric Vincent <aymericvincent%free.fr@localhost>]

Hi,

I started following the pkgsrc-2020Q4 branch and noticed that I need to
put back the line

PYTHON_VERSIONS_ACCEPTED=       27

in the Makefile of x11/qt5-qtwebkit to make it compile[, possibly because
PYTHON_VERSION_DEFAULT is set to 39 in my /etc/mk.conf].

Otherwise the "Source/JavaScriptCore/generate-bytecode-files" python
script fails when trying to pass the "encoding=" parameter to
json.load(). This seems to be a python2-ism.

I'm not sure if it's the correct fix, so I just mention this workaround
FWIW. [Also, I'm not subscribed, cc me if you want to follow up.]

Regards,
 Aymeric