--- Makefile.orig	2020-01-03 23:42:34 UTC
+++ Makefile
@@ -10,8 +10,8 @@ else
 	SDL2CONFIG=sdl2-config
 endif
 
-CFLAGS=-std=c99 -O3 -Wall -Werror -g $(shell $(SDL2CONFIG) --cflags) -Iextern/include -Iextern/src
-LDFLAGS=$(shell $(SDL2CONFIG) --libs) -lm
+CFLAGS += $(shell $(SDL2CONFIG) --cflags) -Iextern/include -Iextern/src
+LDFLAGS += $(shell $(SDL2CONFIG) --libs) -lm
 
 OUTPUT=x16emu