Without that section when building the shared(dll) version of the library you get this error:

test-spawn.obj : error LNK2019: unresolved external symbol _uv_utf8_to_utf16 referenced in function _run_test_environment_creation [C:\Users\Luigi\Documents\GitHub\libuv\run-tests.vcxproj]
test-spawn.obj : error LNK2019: unresolved external symbol _make_program_args referenced in function _run_test_argument_escaping [C:\Users\Luigi\Documents\GitHub\libuv\run-tests.vcxproj]
test-spawn.obj : error LNK2019: unresolved external symbol _quote_cmd_arg referenced in function _run_test_argument_escaping [C:\Users\Luigi\Documents\GitHub\libuv\run-tests.vcxproj]
test-spawn.obj : error LNK2019: unresolved external symbol _make_program_env referenced in function _run_test_environment_creation [C:\Users\Luigi\Documents\GitHub\libuv\run-tests.vcxproj]