timeout: prioritize "timed out" exit status

timeout: prioritize "timed out" exit status

* src/timeout.c (cleanup): Reset the default exit status
to EXIT_TIMEDOUT, if we have in fact received an ALARM.
Otherwise we would exit with status EXIT_CANCELED if
there was an issue writing --verbose output for example.
This also ensures a consistent exit status with ASAN enabled,
as with ASAN stderr is not explicitly closed by gnulib's
close_stdout handler.