Made it possible to force usage of system JPEG libraries.

[zond]

Also made the Debian build rule use it.

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[zond]

@szabadka, @malaterre PTAL at this.

I just added the same workaround for JPEG in the jpegli cmake setup as we already use for e.g. brotli in the jxl cmake setup.

./ci.sh opt now produces build/lib/jpegli/libjpeg.so even with an empty third_party/libjpeg-turbo.

I also made the debian/rules file pick that up.

What I haven't done and don't know how to do: Make the debian build actually depend on libjpeg62-turbo and libjpeg62-turbo-dev.

What else needs to be done?

[malaterre]

What I haven't done and don't know how to do: Make the debian build actually depend on libjpeg62-turbo and libjpeg62-turbo-dev.

I'll do that within debian package only. Thanks

[Traneptora]

libjxl should link to system libjpeg even if jpegli build is enabled. You can test it yourself by encoding a jpeg to a lossless jxl with cjxl, and comparing the result with what happens if you run /usr/bin/djpeg versus djpegli.

[malaterre]

@zond could you please be a little more verbose ? what is going on with this patch ? thanks

[zond]

Sorry, should have explained more.

Since jpegli is moving to https://github.com/google/jpegli/, it's no longer relevant to fix the jpegli build in this repository.

The new PR to fix jpegli build in Debian is google/jpegli#31.