define HAVE_SYS_SOCKET_H if that file is present. This is needed when we

#include "../lib/memdebug.h" for memory debug builds.

src/config.h.in

@@ -26,6 +26,9 @@
 /* Define if you have the <sys/select.h> header file */
 #undef HAVE_SYS_SELECT_H
 
+/* Define if you have the <sys/socket.h> header file */
+#undef HAVE_SYS_SOCKET_H
+
 /* Define if you have the <sys/poll.h> header file */
 #undef HAVE_SYS_POLL_H