Implement LDPT_REGISTER_CLAIM_FILE_HOOK_V2 linker plugin hook [PR109128]

This is one part of the fix for PR109128, along with a corresponding
binutils's linker change.  Without this patch, what happens in the
linker, when an unused object in a .a file has offload data, is that
elf_link_is_defined_archive_symbol calls bfd_link_plugin_object_p,
which ends up calling the plugin's claim_file_handler, which then
records the object as one with offload data. That is, the linker never
decides to use the object in the first place, but use of this _p
interface (called as part of trying to decide whether to use the
object) results in the plugin deciding to use its offload data (and a
consequent mismatch in the offload data present at runtime).

The new hook allows the linker plugin to distinguish calls to
claim_file_handler that know the object is being used by the linker
(from ldmain.c:add_archive_element), from calls that don't know it's
being used by the linker (from elf_link_is_defined_archive_symbol); in
the latter case, the plugin should avoid recording the object as one
with offload data.

	PR middle-end/109128

	include/
	* plugin-api.h (ld_plugin_claim_file_handler_v2)
	(ld_plugin_register_claim_file_v2)
	(LDPT_REGISTER_CLAIM_FILE_HOOK_V2): New.
	(struct ld_plugin_tv): Add tv_register_claim_file_v2.

	lto-plugin/
	* lto-plugin.c (register_claim_file_v2): New.
	(claim_file_handler_v2): New.
	(claim_file_handler): Wrap claim_file_handler_v2.
	(onload): Handle LDPT_REGISTER_CLAIM_FILE_HOOK_V2.

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