> I can try to  modify this block so it just set want_lcms2 to  to no
> automatically if not found, but not sure if manual disable will still
> work in this case


Try attached patch on top of those 3 - should stay enabled if found,
disable otherwise

--without-lcms2

also should work

0001-lcms2-configure-support-for-internal-ffmpeg.patch
0002-Simple-opencolorio-enable-for-ffmpeg-without-testing.patch
0003-Add-very-basic-lcms2-color-management-for-ffmpeg-inp.patch