Add support for NetBSD/sh3 core file sections. Merge multiple copies of auxv...

Add support for NetBSD/sh3 core file sections.  Merge multiple copies of auxv section creation into one function.

	PR 24650
	* elf.c (elfcore_make_auxv_note_section): New function.
	(elfcore_grok_note): Use it.
	(elfcore_grok_freebsd_note): Likewise.
	(elfcore_grok_openbsd_note): Likewise.
	(elfcore_grok_netbsd_note): Likewise.  Plus add support for
	NT_NETBSDCORE_AUXV notes.