bfd_stat_arch_elt buffer overflow

If you manage to put an xcoff object file into a non-xcoff archive
(created by first putting a non-xcoff object file into it), and have
xcoff support compiled into libbfd, then objdump -x on the archive
can segfault.  The problem is that _bfd_xcoff_stat_arch_elt expects
abfd->arelt_data->arch_header to be one of the xcoff variants, but
arelt_data is generated depending on the archive format, *not* the
element format.

	* bfd.c (bfd_stat_arch_elt): Use vector of containing archive,
	if file is an archive element.
	* bfd-in2.h: Regenerate.