Work around perl bug in SvPVutf8().

Work around perl bug in SvPVutf8().

Certain things like typeglobs or readonly things like $^V cause
perl's SvPVutf8() to die nastily and crash the backend. To avoid
that bug we make a copy of the object, which will subsequently be
garbage collected.

Back patched to 9.1 where we first started using SvPVutf8().

Per -hackers discussion. Original problem reported by David Wheeler.