In the other makefiles test_prep (or test-prep) depends on all, so
they shouldn't need updating.
test_prep_pre: preplibrary utilities $(nonxs_ext)
-test_prep: test_prep_pre $(MINIPERL_EXE) $(unidatafiles) $(PERL_EXE) $(dynamic_ext) $(TEST_PERL_DLL) runtests x2p/s2p
+test_prep: test_prep_pre $(MINIPERL_EXE) $(unidatafiles) $(PERL_EXE) $(dynamic_ext) $(TEST_PERL_DLL) runtests x2p/s2p $(generated_pods)
cd t && (rm -f $(PERL_EXE); $(LNS) ../$(PERL_EXE) $(PERL_EXE))
test_prep_reonly: $(MINIPERL_EXE) $(PERL_EXE) $(dynamic_ext_re) $(TEST_PERL_DLL)