PR 33385, Extended Image Header

PR 33385, Extended Image Header

This modifies some of the PR 21813 fixes, allowing for smaller EIHD.
Not knowing any better, I chose to use EIHD__C_LENGTH as the minimum
length.

include/
	* vms/eihd.h (EIHD__C_LENGTH): Comment.
bfd/
	* vms-alpha.c (_bfd_vms_slurp_eihd): Remove size check
	duplicating that done by the caller of this function.
	(alpha_vms_object_p): Allow smaller EIHD.
	(evax_bfd_print_image): Likewise.  Don't print fields past
	the record size.