Use "far" calls and branches so that lld uses valid relocations.

Conditional branch and jump instructions do not always call via PLT
stubs and thus will not honor LD_PRELOAD, etc. lld warns about using
non-preemptible relocations for preemptible or unknown symbols whereas
bfd does not (at least for RISC-V).

Reviewed by: br, James Clarke
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D22658