gcc-4.3 no longer includes this by default, needed to get the ssize_t type.

--- pdsh-2.14/src/modules/machines.c
+++ pdsh-2.14/src/modules/machines.c
@@ -28,6 +28,8 @@
 #  include "config.h"
 #endif
 
+#include <unistd.h>
+
 #include "src/pdsh/wcoll.h"
 #include "src/pdsh/mod.h"
 #include "src/common/hostlist.h"