$NetBSD$

Use X11_LDFLAGS to fix linking.

--- src/Makefile.orig	2020-05-04 04:33:47.000000000 +0000
+++ src/Makefile
@@ -258,7 +258,7 @@ endif
 
 ifeq ($(RENDERER), sdl2gl)
 	RENDER_OBJS = id_vl_sdl2gl.o id_sd_sdl.o id_in_sdl.o
-	LIBS += $(LIBGL)
+	LIBS += $(LIBGL) $(X11_LDFLAGS)
 endif
 
 ifeq ($(RENDERER), sdl2vk)