A couple things need fixing for shared library dependencies to work:

• On Linux a dynamic binary requires a loader. Zig seems to default to assuming a musl loader. The lack thereof, e.g. on Ubuntu, causes a "File not found" error. To fix this the platform needs to be configured to explicitly set the system abi. E.g. on Ubuntu x86_64-linux-gnu would work.
• At least on Linux a dynamic binary does not work if we do not link against libc. Otherwise, executing the binary fails with a segfault.
• The soname of the cc_library produced dynamic binary seems to capture the full output path, at least the Zig linker generates a NEEDED entry with the full path bazel-out/k8-fastbuild/bin/_solib_k8/_U_S_Slink-dependencies_Sshared-library_Cadd___Ulink-dependencies_Sshared-library/libadd_shared.so. However, this path is not always valid, e.g. the result binary may work when executed directly in the workspace root, but it does not work when executed via bazel run or from a different directory. Experiments by invoking zig build-exe directly caused the Zig linker to generate such full path NEEDED entries even when using -ladd_shared flags. It is unclear if there is a set of Zig command-line options that would produce the wanted NEEDED libadd_shared.so and RUNPATH $ORIGIN/... entries. It may be necessary to post-process the produced binary.