patch 8.0.0429: options test does not always test everything

Problem:    Options test does not always test everything.
Solution:   Fix dependency for opt_test.vim.  Give a message when opt_test.vim
            was not found.
diff --git a/src/testdir/Make_ming.mak b/src/testdir/Make_ming.mak
index 8235b95..b95a6ea 100644
--- a/src/testdir/Make_ming.mak
+++ b/src/testdir/Make_ming.mak
@@ -133,4 +133,4 @@
 	@$(DEL) vimcmd
 
 opt_test.vim: ../option.c gen_opt_test.vim
-	$(VIMPROG) -u gen_opt_test.vim --noplugin --not-a-term
+	$(VIMPROG) -u gen_opt_test.vim --noplugin --not-a-term ../option.c