$NetBSD$

Exclude -ldl for NetBSD
https://github.com/berkeley-abc/abc/issues/332

--- Makefile.orig	2024-05-04 04:10:46.000000000 +0000
+++ Makefile
@@ -138,7 +138,7 @@ endif
 
 # LIBS := -ldl -lrt
 LIBS += -lm
-ifneq ($(OS), FreeBSD)
+ifeq ($(filter $(OS), FreeBSD NetBSD),)
   LIBS += -ldl
 endif