/proc/uptime. Fixes the process start time test when run from a container where /proc/uptime is the uptime of the container but the process start time is relative to the host system boot time. Bug #829
drift. For Linux, process start time is relative to boot time, not wallclock time.
resulting timespec as it differs by platform. On most it is wallclock time, on others it is relative to boot time (Linux).