Switch to ELF toolchain readelf(1)

ELF toolchain readelf lacked some functionality at the time other tools
(like size, strip, nm, etc.) were switched over to the ELF toolchain
versions. That has been addressed as of the last update, so we can add
it to the list.

PR: 198950 [exp-run]
Reviewed by: bapt, imp, rpaulo
Relnotes: yes
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D2156