rtld: pass argc/argv/env to dso inits.

This is consistent with how array inits are called, and also makes us
more compatible with glibc environment.

Requested by: Alex S <iwtcex@gmail.com>
PR: 249162
Reviewed by: dim, emaste
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D26351