The problem is the package is linked with clang instead of clang++ because you don't have any c++ files in the package, however libzmq does need to be linked with clang++.
Even fewer external libraries use C++ internally but present a C interface, such as rgeos. These require the C++ runtime library to be linked into the package’s shared object/DLL, and this is best done by including a dummy C++ file in the package sources.
The cross compilation fails on r-universe: https://github.com/r-universe/snoweye/actions/runs/7494400310/job/20402312521
The problem is the package is linked with
clang
instead ofclang++
because you don't have any c++ files in the package, however libzmq does need to be linked with clang++.This case is described in WRE 5.6.1 :
So you can probably fix this problem by creating an empty
src/dummy.cc
similar like https://github.com/cran/rgeos/blob/master/src/dummy.cc