make dynlink.lo depend on reloc.h in makefile

this is mainly a development convenience but will also ensure users
building from latest git always get up-to-date arch-specific dynamic
linker code without having to "make clean".

Makefile

@@ -77,6 +77,8 @@ include/bits/alltypes.h.sh: include/bits
 include/bits/alltypes.h: include/bits/alltypes.h.sh
 	sh $< > $@
 
+src/ldso/dynlink.lo: arch/$(ARCH)/reloc.h
+
 %.o: $(ARCH)/%.s
 	$(CC) $(CFLAGS_ALL_STATIC) -c -o $@ $<