Merge topic 'CMP0126-WARNING'

616972197a Merge branch 'backport-3.21-CMP0126-WARNING' into CMP0126-WARNING
16208ac113 CMP0126: Add control for warnings

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Ben Boeckel <ben.boeckel@kitware.com>
Merge-request: !6282