Allow build to exclude internal avresample

[johnsheu]

This allows the build to complete without using FFmpeg-derived code,
though this disables input resampling and thus requires that input
audio to the fingerprinter is already at the configured fingerprint
sample rate.

[lalinsky]

Hm, we could do this. I just need to verify the resampling configs, to make sure they match. I used the internal copy, because when I was working on the code, I found it to be significantly faster than using libswresample, but maybe things have changed now and with the right settings it could be as fast.

[johnsheu]

Hm, we could do this. I just need to verify the resampling configs, to make sure they match. I used the internal copy, because when I was working on the code, I found it to be significantly faster than using libswresample, but maybe things have changed now and with the right settings it could be as fast.

I'm not sure what you mean by verifying the resampling configs? This PR adds an option to the CMake build to disable the resampling entirely -- so if the user provides audio not in the sample rate of the default config, whatever it is, then analysis fails. The use case I'm thinking of is when the user already has some other facility for doing resampling, and can use that to do preprocessing first.

Also, the check failures look unrelated; I'm not sure how to trigger a rerun.

[wallisch]

Any chance of this getting merged? This would allow the SwiftWrapper to be completely MIT licensed