webkitgtk24: fix compilation failure due to unicode quotes

As reported in this upstream bug...

https://bugs.webkit.org/show_bug.cgi?id=128971

...the pretty unicode double quotes break Python stdin. Backporting the
patch that was attached to that bug report and tweak it minimally to
make it apply on Buildroot.

Fixes:

  http://autobuild.buildroot.net/results/c8e/c8ea1cab0a1ee081f9bca994ff5309ea0117d692/



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>