gnuradio-blocks should not link publicly to libsndfile

[ryanvolz]

What happened?

GNSS-SDR links to gnuradio-blocks, and consuming the existing gnuradio::gnuradio-blocks CMake target requires the downstream library (GNSS-SDR) to link against libsndfile and thus have it as a dependency. This shouldn't be the case, because the use of libsndfile is (as far as I can tell) limited to the internal implementation and headers of the WAV source/sink and is not required to consume any public GNU Radio headers.

The fix would be to move sndfile::sndfile from the PUBLIC to PRIVATE link section for the CMake target: https://github.com/gnuradio/gnuradio/blob/main/gr-blocks/lib/CMakeLists.txt#L184-L199. Doing so would not effect the compilation of GNU Radio itself, so testing of the fix would have to involve re-building the changed GR and ensuring that something linking against gnuradio-blocks does not need the sndfile headers available.

System Information

Ubuntu, but applies to all.

GNU Radio Version

3.10 (maint-3.10)

Specific Version

3.10.3.0

Steps to Reproduce the Problem

Link against gnuradio-blocks using the gnuradio::gnuradio-blocks CMake target.

Relevant log output

No response

[jwmelto]

First observed on Ubuntu 22.04 / GNU Radio 3.10.1
Also present on Fedora rawhide / GNU Radio 3.10.3

Minimizing external linkage is great, but if the linkage is actually required, then the gnuradio packages should depend on their distro-specific sources (libsndfile1-dev for Ubuntu; libsndfile-devel for Fedora).