cygwin: switched back to -std=gnu99
cygwin: switched back to -std=gnu99

* cygwin recently changed their definition of OVERLAPPED
  in winbase.h to using anonymous structs/unions
* anonymous struct unions are a GNU extension and ignored
  in standard C
* this resulted in the OVERLAPPED hEvent handle being
  moved to an improper location, and invalid handle errors

pbatard/libusb-pbatard,pbatard/libusb-pbatard