Respect user variables

--- a/Makefile
+++ b/Makefile
@@ -2,9 +2,5 @@
 # Makefile for Linux Zorro Utilities
 # Copyright (C) 1998--2000 Geert Uytterhoeven <geert@linux-m68k.org>
 
-CC=gcc
-OPT=-O3 -fomit-frame-pointer
-CFLAGS+=$(OPT) -Wall
-
 PREFIX=/usr