Maybe it's better not to explicitly specify CC

dmg/Makefile

@@ -1,6 +1,5 @@
 DMGOBJS=dmg.o base64.o resources.o checksum.o udif.o partition.o io.o zlib-1.2.3/libz.a
 HFSOBJS=../hfs/volume.o ../hfs/btree.o ../hfs/extents.o ../hfs/rawfile.o ../hfs/catalog.o ../hfs/flatfile.o ../hfs/utility.o
-CC=gcc
 CFLAGS=-D_FILE_OFFSET_BITS=64
 
 all: dmg

hfs/Makefile

@@ -1,5 +1,4 @@
 HFSPLUSOBJS=btree.o catalog.o extents.o flatfile.o rawfile.o volume.o utility.o hfs.o
-CC=gcc
 CFLAGS=-D_FILE_OFFSET_BITS=64
 
 all: hfsplus