Remove some hardcoded optimization/warnings flags.  This will become obsolete
with the next release.

--- libdiscmage/Makefile.in.orig	2020-12-26 22:53:30 UTC
+++ libdiscmage/Makefile.in
@@ -22,7 +22,7 @@ INSTALL_DATA=@INSTALL_DATA@
 
 CC=@CC@
 CFLAGS0:=$(CFLAGS) -I. -Wall -W -Wno-implicit-fallthrough \
--Wno-format-truncation -Wno-stringop-overflow -O3 @DEFS@
+@DEFS@
 CFLAGS=$(CFLAGS0) -DDLL
 ifdef DLOPEN
 CFLAGS+=-DDLOPEN