cmTarget: Restore <CONFIG>_LOCATION to CMP0026 OLD behavior (#14808)

Restore support for the undocumented <CONFIG>_LOCATION target property
removed by commit v3.0.0-rc1~175^2 (cmTarget: Remove support for
<CONFIG>_LOCATION property, 2013-12-30) as part of the CMP0026 OLD
behavior.
Merge branch 'master' into CONFIG-LOCATION-CMP0026
cmTarget: Port <CONFIG>_LOCATION support to updated string APIs
Merge topic 'CONFIG-LOCATION-CMP0026' into next

ea17a03b cmTarget: Port <CONFIG>_LOCATION support to updated string APIs
6e466c6f Merge branch 'master' into CONFIG-LOCATION-CMP0026
c903b531 cmTarget: Restore <CONFIG>_LOCATION to CMP0026 OLD behavior (#14808)