Note that lld enables relro by default, so that we already had either
partial or full RELRO, depending on the state of the BIND_NOW knob.
Add a RELRO knob so that the option can be disabled if desired, and so
that builds using the GNU toolchain are equivalent to those using the
standard Clang/LLVM toolchain.
Reviewed by: markj
MFC after: 3 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D35545
2f3a961487