Fix www/qt5-webengine to build on ARM

Fix build for aarch64 and armv7. Chasing Chromium patches into Qt5-Webengine
is a slow process. Multiple build successes have been reported with
this patch, although I have not been able to try it myself.

I hope I got all the attributions right.

PR: 228603 228708
Submitted by: mikael.urankar@gmail.com
Reported by: mikael.urankar@gmail.com, usenet@ulrich-grey.de
Obtained from: mmel