If the cmake user variable COPY_DEPENDENCIES is set, this script will
make it so that a windows build will automatically copy all required
dependencies (FFmpeg, x264, and Qt5) to the respective
additional_install_files\exec(32|64) directory.  This makes it much
easier to set up a development environment on windows, and much easier
to make usable test builds.

It will also copy the appropriate Direct3D compiler DLL, along with
dependencies of dependencies (the icu*.dll and EGL/GLES files for Qt)