Re: Rewrite SHT_GROUP handling

There is no need to loop over the headers twice.  Remove that leftover
from the previous scheme.  Also, the previous scheme silently ignored
a section being mentioned in two or more SHT_GROUP sections.

	* elf.c (process_sht_group_entries): Prevent sections from
	belonging to two groups.
	(_bfd_elf_setup_sections): Process groups in a single loop
	over headers.