Remove bundled zlib.
--- a/src/burner/libretro/Makefile
+++ b/src/burner/libretro/Makefile
@@ -692,6 +692,8 @@
 	LD = $(CXX)
 endif
 
+LIBS += -lz
+
 %.o: %.c
 	$(CC) -c $(OBJOUT)$@ $< $(CFLAGS) $(INCFLAGS)