stand: Recognize SHT_INIT_ARRAY sections as constructor sections

Pass such a section to the kernel using modinfo, otherwise link_elf.c
won't execute constructors for the file. This is required for KASAN,
otherwise redzones for global buffers are not poisoned during boot.

Reviewed by: kib
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D58244