Allow mro_isa_changed_in to be called on nonexistent packages

This is necessary for an upcoming bug fix.

(For this bug:

 @left::ISA = 'outer::inner';
 @right::ISA = 'clone::inner';
 *clone:: = \%outer::;
 print left->isa('clone::inner'),"\n";
 print right->isa('outer::inner'),"\n";

)

This commit actually replaces mro_isa_changed_in with
mro_isa_changed_in3. See the docs for it in the diff for mro.c.

1 files changed, 1 insertions, 0 deletions

diff --git a/hv.h b/hv.h
index 62646b3965..83f90d9a52 100644
--- a/hv.h
+++ b/hv.h
@@ -67,6 +67,7 @@ struct mro_meta {
     (((smeta)->mro_which && (which) == (smeta)->mro_which) \
      ? (smeta)->mro_linear_current			   \
      : Perl_mro_get_private_data(aTHX_ (smeta), (which)))
+#define mro_isa_changed_in(stash) mro_isa_changed_in3(stash, NULL, 0)
 
 /* Subject to change.
    Don't access this directly.