Don't include libbfd.h outside of bfd, part 4

Not much to see here, just renaming a function.

bfd/
	* targets.c (bfd_seach_for_target): Rename to..
	(bfd_iterate_over_targets): ..this.  Rewrite doc.
	* bfd-in2.h: Regenerate.
ld/
	* ldlang.c (open_output): Replace bfd_search_for_target with
	bfd_iterate_over_targets.  Localize vars.