Fix the missing of CancelIoEx

[da-liii]

Fix #228, here is the error:

error: @programdir\modules\private\async\runjobs.lua:256: @programdir\modules\private\action\build\object.lua:91: @programdir\modules\core\tools\gcc.lua:805: In file included from src\tbox\platform\fwatcher.c:37:
src\tbox\platform\windows/fwatcher_iocp.c: In function 'tb_fwatcher_item_free':
src\tbox\platform\windows/fwatcher_iocp.c:81:9: error: implicit declaration of function 'CancelIoEx'; did you mean 'CancelIo'? [-Werror=implicit-function-declaration]
         CancelIoEx(watchitem->handle, &watchitem->overlapped);
         ^~~~~~~~~~
         CancelIo

[da-liii]

The dev branch works fine. And it might be a good idea to include "prefix.h" explicitly.