section_by_target_index memory leak

section_by_target_index memory leak

The rs6000 backend can call coff_section_from_bfd_index from its
object_p function via coff_set_alignment_hook.  If the object doesn't
match, or another target matches too, then the hash table needs to be
freed via a cleanup.

	* coffgen.c (coff_object_cleanup): New function.
	(coff_real_object_p): Return coff_object_cleanup, and call on
	failure path.  Move declaration to..
	* libcoff-in.h: ..here.
	(coff_object_cleanup): Declare.
	* coff-stgo32.c (go32exe_cleanup): Call coff_object_cleanup.
	(go32exe_check_format): Adjust assertion.
	* libcoff.h: Regenerate.