Correct logic for "defined by object"

Correct logic for "defined by object"

The old code missed testing bfd_link_hash_undefweak, and wrongly
excluded bfd_link_hash_common symbols.  It is also clearer to invert
the set of enum bfd_link_hash_type values tested.
bfd_link_hash_indirect and bfd_link_hash_warning will never appear
here.

	* ldexp.c (update_definedness): Correct logic setting by_object.