It’s actually pretty easy to cross-compile qBittorrent on Linux for Windows targets using MXE, a cross environment based on the MinGW-w64 toolchain.
The MinGW-w64 project is an improvement on the original MinGW (Minimalist GNU for Windows) project to support 64-bits targets. Currently MXE supports two MinGW-w64 targets: i686-w64-mingw32 for 32-bits executables and x86_64-w64-mingw32 for 64-bits executables.
This is a guide to cross-compile qBittorrent on Linux for Windows 64-bits only. As usual we’ll use Debian for this.