ffmpeg compile for pd-else on Windows is non-intuitive

[kamomehettapi]

The ffmpeg provided by pd-else is tricky to compile. These are steps I took:

1. Tried to use bash.exe provided by an msys install. However in the ffmpeg_deps custom script failed with Unsupported OS: MSYS_NT-10.0-22631. Seems to only supports mingw64 env according to their script.
2. Installed mingw with choco install mingw instead and used their bash for the bash in the ffmpeg_deps CMakeFiles. Now it complains it can't find make. But mingw names their make mingw32-make.exe for some strange reason. Copied to make.exe on PATH and now it the ffmpeg target builds.

Maybe this can be improved? Or above added to Readme

[porres]

I think @timothyschoen was still trying to figure out how to compile this for PlugData, thanks for your help and report

[kamomehettapi]

Yeah no problem and thanks for the lib !

[kamomehettapi]

Okay I dunno what I changed but now I keep getting

make: *** No rule to make target 'C:\Program', needed by 'libavfilter/allfilters.o'.  Stop.

So that ffmpeg_deps target keeps failing. It seems I only get one shot to build the whole solution without errors, and after that if it tries to rebuild it will attempt to rebuild ffmpeg_deps and fail...

[kamomehettapi]

OK it seems that if I insert make clean before the final make statement in build_ffmpeg.sh it works again