Merge topic 'add_custom_command-arg-handling'

ec519f3e97 add_custom_command: Validate arguments more rigorously
8dc8be0884 AndroidTestUtilities: Remove DEPENDS that was being silently ignored
316840b430 Tests: Add missing POST_BUILD to custom commands
f5f80305ef ExternalProject: Ensure keywords requiring an argument have one

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Merge-request: !9785