The libsocket/libnsl problem is specific to IRIX 4. Confirmed by Tim Rice.
diff --git a/configure.in b/configure.in
index 76061d1..5531360 100644
--- a/configure.in
+++ b/configure.in
@@ -1164,7 +1164,7 @@
 esac
 
 # Most SVR4 platforms (e.g. Solaris) need -lsocket and -lnsl.
-# However on SGI IRIX, these exist but are broken.
+# However on SGI IRIX 4, these exist but are broken.
 # BeOS' sockets are stashed in libnet.
 case "$ac_sys_system" in
 IRIX*) ;;