compile cache.c -mpcrel

Makefile

@@ -99,6 +99,8 @@ $(OBJDIR)/init_fpga.o:	CFLAGS += -mbitfield
 
 # compile printf pc-relative so it can be used as well before and after copy of BaS
 $(OBJDIR)/printf.o:	CFLAGS += -mpcrel
+# the same for flush_and_invalidate_cache()
+$(OBJDIR)/cache.c: CFLAGS += -mpcrel
 
 $(OBJDIR)/%.o:$(SRCDIR)/%.c
 	$(CC) -c $(CFLAGS) $(INCLUDE) $< -o $@