$NetBSD$

NetBSD needs -pthread to build.

--- Makefile.orig	2017-12-11 19:03:21.000000000 +0000
+++ Makefile
@@ -10,6 +10,9 @@ ifeq ($(OS),SunOS)
 CFLAGS += -m32
 CFLAGS += -lnsl -lsocket
 endif
+ifeq ($(OS),NetBSD)
+CFLAGS += -pthread
+endif
 
 PROG = sercons