PR19886, --as-needed regression

PR19886, --as-needed regression

This isn't perfect in checking whether libraries will be loaded since
elf_link_add_object_symbols doesn't recurse down DT_NEEDED links.
(That happens later in ld/emultempl/elf32.em after_open.)  So in
effect this recursive check really only looks one level down the
DT_NEEDED tree.  Which is enough for the most common case, and
libc.so/ld.so in particular.

	PR 19886
	* elflink.c (on_needed_list): Recursively check needed status.
	(elf_link_add_object_symbols): Adjust.