Remove hardcoded optimization flags.

Index: makefile
--- makefile.orig
+++ makefile
@@ -28,7 +28,7 @@
 
 
 SYSTEM=$(shell uname -s)
-CFLAGS=-std=c99 -pedantic -O3 -Wall
+CFLAGS=${FLAGS} -std=c99 -pedantic -Wall
 ifeq ($(SYSTEM),Linux)
 #
 # Linux
