Merged requested to merge mistersandman/cmake:gui_theme_window_fix into master
The QWindowsVistaStyle moved into a separate plugin in Qt 5.10 (see https://code.qt.io/cgit/qt/qtbase.git/commit/?id=4f3249f32dbe5c20aabbfd9b4f9c558aaf449e48).
We need to link explicitly against this plugin now after updating to Qt 5.12 (!3079 (merged)).
Note: There might be other missing libraries to link against in
win64_release.cmake, but I can't test this, since the specific Qt configurations for the release builds are not public (#19103 (closed)).
Fixes: #19147 (closed)