ifuncs can be only called in the (early boot) kernel environment, so
postpone resolving until early stage of the kernel boot. This commit
is performed in advance to make loaders on most machines updated
before ifuncs appear in the kernels.
Reviewed by: emaste, jhb
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D13838
latter aren't used. Prefer sys/link_elf.h to link.h so we're only
dependent on the kernel tree. The default installation of link.h just
includes this file, and any benefit from that is outweighed by the
hassle it causes. This reduces the footprint of files needed from the
system includes (or sysroot in buildworld).
Sponsored by: Netflix
