Enable ld.lld as bootstrap linker by default on i386

Akin to r327783 for amd64. lld has been usable for amd64 for quite some
time, but a couple of issues remained that affected i386. These were
recently addressed upstream in lld and merged into FreeBSD or addressed
directly in FreeBSD (r326831, r326879, r326897, r326957, r333401,
r334626, r336664).

Similarly to the intial amd64 commit this change enables lld only as the
bootstrap linker (used to link the kernel and userland libraries and
executables), while GNU ld.bfd is still installed as /usr/bin/ld and
used for ports builds. That will be changed shortly, after an exp-run.

This is a recommit of r327823 after additional lld fixes.

PR: 225128 (exp-run)
Relnotes: Yes
Sponsored by: The FreeBSD Foundation