Commit c389f8bb (cmLocalGenerator: Port Find method away from
GetGeneratorTarget, 2015-10-25) ported the implementation of
FindGeneratorTargetToUse away from the FindTargetToUse method,
but neglected to handle alias targets.

The latter method has a parameter to determine whether to
include alias targets in the search, but as that is only
needed at configure time, this generate-time equivalent does
not need the condition.