[perl #120694] Fix ->SUPER::foo and AUTOLOAD

Commit aae438050a20 (5.17.4) broke ->SUPER::foo with AUTOLOAD by look-
ing up AUTOLOAD from the current package, rather than the current
package’s superclass.

Instead of keeping track of whether it was doing a SUPER lookup via a
::SUPER prefix on the package name, that commit changed method lookup
to pass a GV_SUPER flag around (to fix another bug) and to pass the
current stash, rather than __PACKAGE__::SUPER.  But it did not update
gv_autoload_pvn to pass that flag through to gv_fetchmeth_pvn when
actually looking up the method.