Remove hardcoded optimization flags.

--- libdiscmage/Makefile.in.orig	2021-12-17 09:58:17 UTC
+++ libdiscmage/Makefile.in
@@ -23,7 +23,7 @@ INSTALL_DATA=@INSTALL_DATA@
 ifeq ($(CC),cc)
 CC=@CC@
 endif
-CFLAGS0:=$(CFLAGS) -I. -Wall -W -Wno-implicit-fallthrough -O3 @DEFS@
+CFLAGS0:=$(CFLAGS) -I. -Wall -W -Wno-implicit-fallthrough @DEFS@
 ifneq ($(findstring clang,$(CC)),clang)
 CFLAGS0+=-Wno-format-truncation -Wno-stringop-overflow
 endif