Fixing warnings uncovered by Clang 15.0 on macOS 14.7.1.

[rptb1]

Fixing the build errors seen in e.g. this GitHub build output which says

/Users/runner/work/mps/mps/code/trans.c:154:9: error: variable 'added' set but not used [-Werror,-Wunused-but-set-variable]
(2 failures)
  Count added = 0;

The "added" count variable has been around since Perforce changelist 178798 in 2012, before transforms were released to Configura in MPS 1.110. It does not appear to ever have been used for anything.

[rptb1]

According to the build output, we have a longer list of enabled warnings in the MPS Xcode project than in our make files. However, copying that list to ll.gmk and doing, e.g.

CC=clang-15 make -f lii6ll.gmk VARIETY=cool NOISY=true clean lii6ll/cool/trans.o

does not produce the build error on Ubuntu 22.04. So something is different about the Clang 15.0 on Ubuntu vs macOS/Xcode.

rb@kiwi:~/git/mps/code$ clang-15 --version
Ubuntu clang version 15.0.7
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

It's a shame, because it would be nice to get an early warning of macOS issues when working on Linux!

[rptb1]

Executing proc.review.express.

1. Start time 11:33.
2. Applied entry.universal and entry.impl. The build now succeeds on GitHub's macos-latest runner.
3. Calling in @thejayps . There will be a short delay.

[rptb1]

Executing proc.review.check.

1. Start time 12:37.
2. No defects found.
3. End time 12:44.

[thejayps]

Checking: m1: assume.parked in line 162, code then goes on to AVER arena is clamped, which is at face value a different state to parked. The following line AVER(arena->busyTraces == TraceSetEMPTY); then does check that no traces are running, so the arena is parked. But there is a clarity issue here, where we have 2 distinct states and appear to be checking for the wrong one.

[thejayps]

ignore ... comment below not intended for this pr

"Checking - no defects found after 6 minutes"

[thejayps]

Checking - no defects found after 6 minutes

[rptb1]

Continuing proc.review.express.
4. Made a minor clarifying edit in pair with @thejayps.
5. Waited for automated checks to complete as expected.
6. proc.review.exit.pass: Revised change passed.
7. proc.review.exit.calc: about 40 minutes used.

[thejayps]

@rptb1 has done exit.pass

[rptb1]

Executing proc.merge.pull-request.

1. Start time 13:20.
2. Merged and ran local ci tests before pushing.
3. End time 13:27.

[rptb1]

Hmm, GitHub didn't close this PR when we merged the changes, resulting in 9fd0577 . During merge I did proc.merge.pull-request section 5 step 6, git pull --rebase=merges github, in order to catch up to master. This did not do what we expect, because it changes the hashes of the commits. So the procedure doesn't produce the intended effect. This is input to #228 .