This Qt release "pluginized" the backends for TLS support so we need to
make sure to link against at least one TLS plugin since all of my
applications which use Qt Network expect TLS to work.
* Making an Android APK should now generally work with NDK r21.d and
Qt 5.15.1 and CMake 3.18 although some details might still need tweaking
* It is now supposed to be used within the NDK's toolchain instead of
CMake's built-in Android support (which makes problems with newer NDK
versions)
* The old way to lookup/pass variables is preserved so it should still
work with older Qt versions and CMake's built-in Android support
* Qt's own support for invoking androiddeployqt needed to be disabled
because it lead to CMake errors (see comment)