BFD/XCOFF: Fix storage class setting for weak defined symbols

BFD/XCOFF: Fix storage class setting for weak defined symbols

Fix an issue with commit 8602d4fea60d ("Add AIX weak support"),
<https://sourceware.org/ml/binutils/2009-03/msg00189.html>, and use the
correct condition to set the storage class for weak defined symbols.

The context here is as follows:

  else if ((h->root.type == bfd_link_hash_defined
            || h->root.type == bfd_link_hash_defweak)
           && h->smclas == XMC_XO)
    {
      BFD_ASSERT (bfd_is_abs_section (h->root.u.def.section));
      isym.n_value = h->root.u.def.value;
      isym.n_scnum = N_UNDEF;
      if (h->root.type == bfd_link_hash_undefweak
          && C_WEAKEXT == C_AIX_WEAKEXT)
        isym.n_sclass = C_WEAKEXT;
      else
        isym.n_sclass = C_EXT;
      aux.x_csect.x_smtyp = XTY_ER;
    }

so clearly the inner condition can never be true.  Correct the condition
then to check for the `bfd_link_hash_defweak' symbol type instead here,
and in a similar place a little further down in the same function.

	bfd/
	* xcofflink.c (xcoff_write_global_symbol): Fix symbol type
	checks for defined weak symbols.