Hojun-Cho
44c47c3ea0
build_one/buildone gain an explicit objstem: 'ww build -o X' derives
main.{combined.ww,s,o} beside X; 'ww run' uses its per-pid /tmp stem;
default no--o stays next-to-source (load-bearing for the make regen of
tracked combined.ww and the freshness gate). Realizes the redirect TODO
in 995_self_rebuild.c. Kills the concurrent-test torn-read race on
selfhost/cmd/<tool>/main.* (the 991 transient). 993/995/949 pass -o
into their per-pid workdirs; 949's '-o /dev/null' relied on the old
driver ignoring -o (audited: the only live driver case). Atomic
combined write (os.rename) deferred to its own commit - lib/os lacks
rename and that addition is an import-floor regen.