Needed for setsockopt() and socketpair().

--- protobuf-30.2/cmake/tests.cmake.orig
+++ protobuf-30.2/cmake/tests.cmake
@@ -100,6 +100,7 @@
 endif ()
 
 add_executable(tests ${tests_files} ${common_test_files})
+target_link_libraries(tests socket nsl)
 if (MSVC)
   target_compile_options(tests PRIVATE
     /wd4146 # unary minus operator applied to unsigned type, result still unsigned