* 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/poll.cc

@@ -12,6 +12,7 @@
 #include <sys/time.h>
 #include <sys/poll.h>
 #include <errno.h>
+#include <stdlib.h>
 #include "security.h"
 #include "fhandler.h"
 #include "path.h"