$OpenBSD$

Ignore CFLAGS from MAKE_ENV.  Without this patch, simutrans was
combining CFLAGS and CXXFLAGS but makeobj was using CXXFLAGS only.

Index: Makefile
--- Makefile.orig
+++ Makefile
@@ -1,3 +1,4 @@
+CFLAGS =
 CFG ?= default
 -include config.$(CFG)
 
