I actually did this because it makes it a bit easier to use with a
build from cross-compiled windows FFMpeg/x264 DLLs. When compiling on
linux I just have it compile to a custom prefix directory for the
specific windows arch, then I just copy the arch dir back to my windows
HD when complete. Adding this to the cmake allows me to use the compile
arch directories directly without modification.
This can make it a bit easier to set up 32bit/64bit environments
separately on windows. This simply allows you to additionally set
FFmpegPath32, FFmpegPath64, x264Path32, x264Path64, etc.