[FIX ERROR] ISO C90 forbids mixed declarations and code and SyntaxError

In file included from gevent/gevent.core.c:237:0:
gevent/libev.h: In function ‘gevent_ev_default_loop’:
gevent/libev.h:22:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
cc1: some warnings being treated as errors

SyntaxError: invalid syntax