near the top of win32.c
Of course you must also add the check(s) (there's a conditional compilation there) for the return val WAIT_TIMEOUT now, in addition to the check for WAIT_FAILED...
Ah, but you need to put it in a *.h file that will be
included by the Posix module so that it will know that
your vendor now does define WNOWAIT.
(short pause while I double check something before
opening my big mouth -- something I almost never do)
Posix.pm #include's perl.h which #include's config.h
so the definition of WNOHANG needs to be added to each
of the win32/config_H.* files except win32/config_h.PL.