Fix section dumping so that warnings are not issued for missed sections in...

Fix section dumping so that warnings are not issued for missed sections in separate debuginfo files.

	PR 27478
	* readelf.c (dump_section_as_strings): Mention separate filename.
	(dump_section_as_bytes): Likewise.
	(dump_section_as_ctf): Likewise.
	(initialise_dumkps_byname): Only issue a warning for missing
	sections if processing the main file.
	(process_section_contents): Only issue a warning for unsumped
	section numbers in the main file.
	(initialise_dump_sects): New function.  Contains code extracted
	from ...
	(process_object): ... here.  Also call initialise_dump_sects for
	separate files.