Saving more binary size with a stricter ffmpeg configuration.

Hello, I was investigating this build process as part of some research for a Chrome bug:
https://bugs.chromium.org/p/chromium/issues/detail?id=1090959#c4

FFmpeg offers quite a few more flags that you can try disabling to save more binary size:
https://chromium-review.googlesource.com/c/chromium/third_party/ffmpeg/+/2240305/1/build-js.sh#16

Depending on your application you can avoid compiling ffmpeg.c too and just use the API methods for the functionality you desire:
https://chromium-review.googlesource.com/c/chromium/third_party/ffmpeg/+/2240305/1/mux_demux_methods.cc

Just FYI in case this helps with download size. Apologies for the noise if you're already tried this without effect.