> - when importing fcntl, bear in mind that some systems don't have this
> module (e.g. Windows), so you should catch and silence the ImportError

would something like the following be ok?:

try:
    import fcntl
except ImportError:
    fcntl = False

and then:

if hasattr(socket, "SOCK_CLOEXEC") and fcntl:
    tests.append(CloexecLinuxConstantTest)