--- Makefile.orig	2017-11-07 19:42:14 UTC
+++ Makefile
@@ -1,10 +1,11 @@
-CC=gcc
-CFLAGS=-g -Wall -O2 -Wno-unused-function
+CC ?=		gcc
+CFLAGS ?=	-g -Wall -O2 -Wno-unused-function
+LDFLAGS +=	-lz -lm
 
-all:seqtk
+all: seqtk
 
-seqtk:seqtk.c khash.h kseq.h
-		$(CC) $(CFLAGS) seqtk.c -o $@ -lz -lm
+seqtk: seqtk.c khash.h kseq.h
+	$(CC) $(CFLAGS) seqtk.c -o $@ $(LDFLAGS)
 
 clean:
-		rm -fr gmon.out *.o ext/*.o a.out seqtk trimadap *~ *.a *.dSYM session*
+	rm -fr gmon.out *.o ext/*.o a.out seqtk trimadap *~ *.a *.dSYM session*