Build separate 32bit and 64bit builds for Windows, don't ship ffmpeg twice

[brian-mann]

Currently we only build 32bit Windows, but we ship two versions of ffmpeg for both 32bit and 64bit Windows.

This inflates the binary by almost 100mb O_O.

Need to build separate Windows arch. We've already updated the CLI and the download server to account for this.

[flotwig]

Related issue: #3888