Update plugin_maybe_claim

Update plugin_maybe_claim

This patch removes the argument of pointer to struct ld_plugin_input_file.
This is the first step to extract a plugin_object_p out of
plugin_maybe_claim for BFD.

	* plugin.c: Include "libbfd.h".
	(plugin_strdup): New.
	(plugin_maybe_claim): Remove the argument of pointer to struct
	ld_plugin_input_file.  Open and handle input entry.
	* plugin.h (plugin_maybe_claim): Updated.
	* ldfile.c (ldfile_try_open_bfd): Call plugin_maybe_claim directly
	without passing a pointer to struct ld_plugin_input_file.
	* ldmain.c: Don't include "libbfd.h".
	(add_archive_element): Call plugin_maybe_claim directly without
	passing a pointer to struct ld_plugin_input_file.