Guarantees to evaluate sv only once; use the more efficient C<SvPVbyte>
otherwise.
+=for apidoc Am|bool|SvIsCOW|SV* sv
+Returns a boolean indicating whether the SV is Copy-On-Write. (either shared
+hash key scalars, or full Copy On Write scalars if 5.9.0 is configured for
+COW)
+
+=for apidoc Am|bool|SvIsCOW_shared_hash|SV* sv
+Returns a boolean indicating whether the SV is Copy-On-Write shared hash key
+scalar.
=cut
*/