Building gstreamer trunk on Windows, from MSVC 2019 fails (libffi not found)

Tried building trunk, failed on libffi dependency, not pulled in by build system. Located libffi, its a nightmare to build on Windows, msvc. Found the following fork : https://github.com/am11/libffi/tree/feature/cmake-build-configs ... which contains cmake configuration scripts to configure & build dependency using cmake. So this could be integrated into the automated build process.

Have requested these cmake config scripts are added to libffi trunk so we don't have to use a fork.

https://github.com/libffi/libffi/issues/582

As I have libffi compiling, will try to complete a Windows MSVC build :)