 - drop unknown warning -Wformat-overflow=0
 - drop hardcoded -O2

Index: Makefile
--- Makefile.orig
+++ Makefile
@@ -62,7 +62,7 @@ ifeq ($(DEBUG),YES)
 cflags += -g -Og
 cppflags += -DENABLE_PLAYBACK_SWITCH
 else
-cflags += -O2
+cflags +=
 endif
 
 # Add user-provided flags.
