When the necessary libraries are not present in a standard search path, Gnuastro's configure script will also search for them in the same directory that Gnuastro will be installed.

For example this is the output line of ./configure for a custom-build CFITSIO:

checking for libcfitsio... yes
checking how to link with libcfitsio... -L/path/to/custom/install/dir/lib -lcfitsio

But since we are intentionally not adding RPATH, when trying to run the programs built in this way, on macOS we get a linking error, for example this line in 'config.log' for the test of 'getgroups':

dyld: Library not loaded: libcfitsio.8.dylib
Referenced from: /current/build/dir/gnuastro-0.9.58-5cc8/./conftest
Reason: image not found

The interesting situation is that LD_LIBRARY_PATH has not been set. But it is also not used in macOS. However, setting DYLD_LIBRARY_PATH and DYLD_FALLBACK_LIBRARY_PATH for macOS also didn't fix this problem.