liblinphone was broken by 1769609dc0 as
zxing-cpp 2.0 and later require C++ 17 [1]. The version of liblinphone
in nixpkgs does however only build with C++ 14. This was then fixed in
c42909d342 by disabling QR code support.
Its master branch does however build with C++ 17, so backport that
commit. Due to upstream running formatters on their code in the
meantime, the backport had to be done manually and the commit cannot be
picked.
[1] https://github.com/zxing-cpp/zxing-cpp/releases/tag/v2.0.0
ae8f0d7b1e