WIP: Android support

[mappu]

This PR adds Android build support for Eiskalt DC++.

Seems strange, but it's quite cool to use. Especially if you have an Android tablet with bluetooth keyboard.

1. Enter the docker container that we use as a workspace:
   • docker run -it --rm --volume="${PWD}:/home/user/project" rabits/qt:5.15-android /bin/bash
   • The rabits/qt:5.15-android docker container is used for the Qt Widgets Android port and Android SDK / NDK installation.
2. Run ./xcompile2.sh make-apt-deps.
   • This found docker container is quite nice but still missing some important tools.
3. Run ./xcompile2.sh make-deps.
   • This will build, patch, and compile bzip2, openssl, libpcre, libidn2 for Android inside the current working directory.
4. Run ./xcompile2.sh make-native.
   • This will build eiskaltdcpp and link it as an APK.
   • You likely need to run this 2x and also run the commented-out link command to generate the final libeiskaltdcpp-qt.so file. I couldn't convince ninja to generate it properly. Despite that there are already some rough sed patches to the generated ninja file.

I have left this PR as WIP because my changes to the CMake files were quite destructive. I think it needs more work to properly integrate with the CMake build toolchain, many optional libraries are disabled, and probably many commits should be squashed. It only builds for ARM32 owing to a bug in the ARM64 linker in this version of the Android SDK (see the last 4 commits starting with a1f39b2). But it may be an interesting starting point.

[mappu]

Here attached is a working Android binary to try.

eiskaltdcpp-qt-beta.apk.zip