* exceptions.cc: Add stdlib.h include for alloca declaration.

* poll.cc: Ditto.
* termios.cc: Ditto.
* syscalls.cc (_write): Only allow zero length when fd is valid.

winsup/cygwin/termios.cc

@@ -14,6 +14,7 @@ details. */
 #include "winsup.h"
 #include <errno.h>
 #include <signal.h>
+#include <stdlib.h>
 #include "cygerrno.h"
 #include "security.h"
 #include "fhandler.h"