Add &CORE::glob

Add &CORE::glob

I added a special case for OP_GLOB to pp_coreargs, since glob does not
have the u flag in regen/opcodes; hence PL_opargs[opnum] & OA_DEFGV is
false, even though glob does imply $_.

Adding the flag to regen/opcodes is not so simple, as the code in
ck_fun that adds the DEFSV op does not account for list ops, but
leaves op_last unchanged.

Changing ck_fun to account requires adding more code than this special
case in pp_coreargs.

OPf_SPECIAL indicates that glob was called with the CORE:: prefix.