Rearrange and fix whitespace.
Improve readability
Unbreak builds without sb-thread feature
compiler/sparc/subprim: Change LENGTH/LIST to use non-continuable errors.

  * There's a small stack of more to be done here, but the use of
continuable errors, while supported at least somewhat by the
runtime, simply isn't supported by the debugger, so there's no
point in using them over the non-continuable errors...  And these
are the last two use sites for continuable errors on SPARC.

  * There are a few more opportunities for excellence here, but
there are some fiddly little details involved, so they call for
separate commits.
compiler/sparc/macros: Kill the continuable-error trap noise.

  * We don't use continuable error traps anywhere, and the
debugger doesn't support them.  If anyone wants to resurrect such
support (and I can see it as a possibility), they can either dig
the old code out of source control or re-derive it themselves.
Move SPARC over to slimmed-down EMIT-ERROR-BREAK interface, part 1.

  * The prep-work has already been done in eliminating the
continuable error bits, now it's time for the first part of the
main show: adjusting the INTERFACE parts.

  * For this part we're just pushing a QUOTE from the guts of a
macro code generation function out to the call sites, matching the
other platforms that have already made this change.  We'll do the
actual implementation damage in part 2.
compiler/generic/array: Invert conditionals for EMIT-ERROR-BREAK changes.

  * This is the halfway point for these changes: Fully half of the
backends are on the new version of the interface while half are
still on the old version.

  * Instead of having the conditionals list the platforms that
have been updated (a list that can only grow), list the platforms
that have NOT been updated (a list that can be expected to shrink).
Move SPARC over to slimmed-down EMIT-ERROR-BREAK interface, part 2.

  * Now that the noisy touch-lots-of-files work has been done, we
can settle in to do the harder-to-validate bits that are entirely
contained within a single file.

  * Based somewhat on the PPC version in 1.0.28.16, with a
slightly different choice of implementation strategy, and a result
that hews closer to the code originally replaced.
compiler/sparc/subprim: Clean up a FIXME in LENGTH/LIST.

  * There's a longstanding FIXME in this code, due to it using two
type tests each time through the loop, even though one can only
ever trigger on the first iteration, and due to PPC being the only
other backend that does so.

  * Actually, it's worse than that: That type test that can only
trigger on the first iteration?  It can't, thanks to the VOP
:ARG-TYPES parameter...  Well, unless someone gets really careless
with their low-SAFETY code.

  * First, change the out-of-line error trap to use PTR rather
than OBJ.  Means the debugger can't always point out a variable at
fault, but also means that we only need the one error trap.  And,
as mentioned above, it'd take someone doing something broken at
low SAFETY for it to matter anyway.

  * Second, kill the inline error trap and its type test.

  * Third, do a partial unroll and loop rotation, putting the exit
test at the end so that we can do fall-through exit, and
duplicating it at the beginning so that we don't need to jump into
the middle of the loop body.

  * And the entire approach, with the exception of the use of
branch-delay slots, can also be done on PPC...  But not in this
commit.