* config/obj-elf.c: (obj_elf_change_section): Add "group" param.

	Set elf_section_data group from it.  Warn if group name changed.
	(obj_elf_parse_section_letters): Parse 'G' too.
	(obj_elf_section): Parse group name.
	(struct group_list): New.
	(build_group_lists): New function.
	(elf_frob_file): Create SEC_GROUP section(s).

	* config/obj-elf.c: (elf_copy_symbol_attributes): Zap trailing
	whitespace.