MFC r255077:

acpi_thermal: Warn about insane _TMP temperature only once

A warning is emitted again if the temperature became briefly valid
meanwhile. This avoids spamming the user when the sensor is broken.

Other values (ie. not _TMP) always raise a warning.
MFC r259729:
  Bootstrap etcupdate(8) as part of the release build, similar
  to what is done for mergemaster(8).  This allows etcupdate(8)
  to work out-of-box after the first upgrade of a system.

Sponsored by:	The FreeBSD Foundation