Fix freeing of link_info.hash

ld:
	* ldlang.c (lang_finish): Don't call bfd_link_hash_table_free here.
	(output_bfd_hash_table_free_fn): New variable.
	(open_output): Save the _bfd_link_hash_table_free function for the
	output_bfd into output_bfd_hash_table_free_fn.
	* ldmain.c (ld_cleanup): If set, call output_bfd_hash_table_free_fn
	on link_info.hash.
	* ldlang.h (output_bfd_hash_table_free_fn): Declare.

ld/testsuite:
	* ld-mmix/wrap1.d, ld-mmix/wrap1a.s, ld-mmix/wrap1b.s,
	ld-mmix/wrap1c.s, ld-mmix/wrap2.d, ld-mmix/wrap3.d,
	ld-mmix/wrap3a.s, ld-mmix/wrap3b.s, ld-mmix/wrap4.d: New
	tests.