modernize: manage cmCommand instances using unique_ptr.

Source/cmCMakeHostSystemInformationCommand.h

@@ -9,6 +9,8 @@
 #include <string>
 #include <vector>
 
+#include "cm_memory.hxx"
+
 #include "cmCommand.h"
 
 class cmExecutionStatus;
@@ -28,9 +30,9 @@ public:
   /**
    * This is a virtual constructor for the command.
    */
-  cmCommand* Clone() override
+  std::unique_ptr<cmCommand> Clone() override
   {
-    return new cmCMakeHostSystemInformationCommand;
+    return cm::make_unique<cmCMakeHostSystemInformationCommand>();
   }
 
   /**