MFC r296419 (by kib):

In the link_elf_obj.c, handle sections of type SHT_AMD64_UNWIND same
as SHT_PROGBITS. This is needed after the clang 3.8 import, which
generates that type for .eh_frame section, which had SHT_PROGBITS type
before.

Reported by: Nikolai Lifanov <lifanov@mail.lifanov.com>
PR: 207729
Tested by: dim (previous version)
Sponsored by: The FreeBSD Foundation

MFC r296428:

Since kernel modules can now contain sections of type SHT_AMD64_UNWIND,
the boot loader should not skip over these anymore while loading images.
Otherwise the kernel can still panic when it doesn't find the .eh_frame
section belonging to the .rela.eh_frame section.

Unfortunately this will require installing boot loaders from sys/boot
before attempting to boot with a new kernel.

Reviewed by: kib