The following patch helps in the case when a sockets library is installed; in my case, ls080b.zip from the DJGPP site:
=== modified file 'src/msdos.c'
--- src/msdos.c 2014-08-09 16:12:33 +0000
+++ src/msdos.c 2014-08-09 21:51:56 +0000
@@ -4016,7 +4017,7 @@
#endif
-#ifndef HAVE_SELECT
+#ifndef HAVE_SYS_SELECT_H
#include "sysselect.h"
/* This yields the rest of the current time slice to the task manager.
The reasoning is that having select doesn't imply having the sys/select.h functionality that the following code emulates.