Remove optimization flags for debug or release builds

Index: src/Makefile
--- src/Makefile.orig
+++ src/Makefile
@@ -12,11 +12,9 @@ endif
 
 ifeq ($(debug),yes)
     CPPFLAGS += -DKAK_DEBUG
-    CXXFLAGS += -O0
     suffix := .debug
 else
     ifeq ($(debug),no)
-        CXXFLAGS += -O3
         suffix := .opt
     else
         $(error debug should be either yes or no)