On macOS High Sierra, building via MacPorts:
:info:build types.sip:30:56: error: ordered comparison between pointer and zero ('PyObject *' (aka '_object *') and 'int')
:info:build if (obj == NULL || PyList_SET_ITEM (l, i, obj) < 0)
:info:build ~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~
:info:build 5 warnings and 1 error generated.
:info:build error: command '/usr/bin/clang' failed with exit status 1
See bug report at MacPorts.
(I cannot confirm this personally, as I haven't got High Sierra yet.)