qt-build-system wraps variables such as QT_PLUGIN_PATH  with  '= instead of prefix, so when qtwayland is installed in a profile or included in the environment, the application fails to see it. Programs run with export QT_QPA_PLATFORM=wayland-egl will fail to launch.

We could:

1. Use 'prefix so that the parent environment's variables are appended and users have to manually install qtwayland them selves.
   
2. Include qtwayland as an input to every qt package somehow. Can the build system do that? Considering that Wayland seems to be the future, I feel that Qt GUI applications should support it by default. I mean, wayland is in the closure of qtbase anyway.
3. Both? Why is '= used anyway?
   

How should this be done?