Build err on OS X

[Igor]

Hi, build latest git head, error like:

src/listener.c:361:5: warning: implicit declaration of function
'fcntl' is invalid in C99 [-Wimplicit-function-declaration]
                                fcntl(cfd, F_SETFL, O_NONBLOCK);

                                ^
src/listener.c:361:16: error: use of undeclared identifier 'F_SETFL'
                                fcntl(cfd, F_SETFL, O_NONBLOCK);


Bests,
-Igor