Fix and enable warnings -Wunreachable-code

[mspang]

• Fix or remove loops that run at most once
• Add a quit variable in Android IO thread; otherwise the code after the
  loop is [more obviously] unreachable.
• Don't use enums as test parameters that can only be changed by editing
  the test. Perhaps we shouldn't have these at all, but static constexpr
  triggers no diagnostics.

[github-actions]

Size increase report for "gn_qpg6100-example-build" from 8997367

File	Section	File	VM
chip-qpg6100-lock-example.out	.text	32	32

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-qpg6100-lock-example.out and ./pull_artifact/chip-qpg6100-lock-example.out:

sections,vmsize,filesize
.debug_line,0,55
.debug_loc,0,42
.text,32,32
.debug_frame,0,12
.debug_info,0,-5
.debug_ranges,0,-24
.debug_abbrev,0,-28
[Unmapped],0,-32