gcc-4.3 no longer includes this by default.

--- libpq++-4.0/pgdatabase.cc
+++ libpq++-4.0/pgdatabase.cc
@@ -15,6 +15,8 @@
 *-------------------------------------------------------------------------
 */
 
+#include <cstdlib>
+
 #include "pgdatabase.h"
 
 #ifdef HAVE_NAMESPACE_STD