Remove hardcoded optimization flags.

--- Makefile.orig	2021-12-17 09:54:12 UTC
+++ Makefile
@@ -11,7 +11,7 @@ endif
 CFLAGS0:=$(CFLAGS)
 include config.mak
 
-CFLAGS+=-I. -Wall -W -Wno-implicit-fallthrough -O3 -fsigned-char
+CFLAGS+=-I. -Wall -W -Wno-implicit-fallthrough -fsigned-char
 ifneq ($(findstring clang,$(CC)),clang)
 CFLAGS+=-Wno-format-truncation -Wno-stringop-overflow
 endif