--- Makefile.orig	2021-01-31 12:40:57.000000000 +0100
+++ Makefile	2021-07-26 19:54:17.000000000 +0200
@@ -1,11 +1,11 @@
-CC=gcc
-CFLAGS=-O3 -Wall -Wextra -Wno-unknown-pragmas -Wcast-qual
+CC?=gcc
+CFLAGS+=-O3 -Wall -Wextra -Wno-unknown-pragmas -Wcast-qual
 LDFLAGS=
 # CFLAGS=-O3 -Wall -Wextra -Wno-unknown-pragmas -Wcast-qual -g -fsanitize=thread
 # LDFLAGS=-g -fsanitize=thread
 # CFLAGS=-O3 -Wall -Wextra -Wno-unknown-pragmas -Wcast-qual -g -fsanitize=address
 # LDFLAGS=-g -fsanitize=address
-LIBS=-lm -lpthread -lz
+LIBS+=-lm -lpthread -lz
 ZOPFLI=zopfli/src/zopfli/
 ZOP=deflate.o blocksplitter.o tree.o lz77.o cache.o hash.o util.o squeeze.o katajainen.o symbols.o