Since ninja 1.8.0[0] and samurai 0.2[1], output mtime is always
recorded after a job succeeds, and outputs are considered dirty if
the recorded mtime is older than any input. This means that even
if a command partially writes its output then fails (for example,
if run with stdout redirected to a file), it will still get re-run
during the next build.
This means that outputs no longer have to be written atomically
(i.e. renamed into place) in order to ensure a correct build, and
we can drop the idiom `command >$out.tmp && mv $out.tmp $out`.
[0] 04d886b110
[1] 799bc5a471
