Remove hardcoded optimization flags.

--- backup/libcd64/Makefile.orig	2021-12-17 09:47:00 UTC
+++ backup/libcd64/Makefile
@@ -10,7 +10,7 @@ endif
 ifdef DEBUG
 CFLAGS+=-pg -g -pedantic -ansi -DDEBUG
 else
-CFLAGS+=-O3 -funroll-loops
+CFLAGS+=-funroll-loops
 ifneq ($(findstring clang,$(CC)),clang)
 CFLAGS+=-fexpensive-optimizations
 endif