Properly handle note sections and segments

Properly handle note sections and segments

When dumping notes, get note alignment from either note section or note
segment.  To support notes generated by assemblers with

https://sourceware.org/bugzilla/show_bug.cgi?id=22492

we treate alignment as 4 bytes if it is less than 4.  Otherwise, we skip
notes if alignment isn't 4 nor 8 bytes.

We should call load_separate_debug_file only if e_shstrndx != SHN_UNDEF.

	PR binutils/22490
	* readelf.c (process_notes_at): Add an argument for note
	alignment.  If note alignment is less than 4, use 4 byte
	alignment.  Otherwise, skip notes if alignment isn't 4 nor
	8 bytes.
	(process_corefile_note_segments): Pass segment alignment to
	process_notes_at.
	(process_note_sections): Pass section alignment to
	process_notes_at.
	(process_object): Call load_separate_debug_file only if
	e_shstrndx != SHN_UNDEF.