--- ./Makefile.orig	2021-02-04 19:47:43.746288080 +0000
+++ ./Makefile	2021-02-04 19:48:32.749583554 +0000
@@ -1,5 +1,5 @@
-CC=gcc
-CFLAGS=-O3 -Wall -Wextra -Wno-unknown-pragmas -Wcast-qual
-LDFLAGS=
+CC?=gcc
+CFLAGS+=-Wall -Wextra -Wno-unknown-pragmas
+LDFLAGS?=
 # CFLAGS=-O3 -Wall -Wextra -Wno-unknown-pragmas -Wcast-qual -g -fsanitize=thread
 # LDFLAGS=-g -fsanitize=thread