New ninja subtool to return the "dirty" state of a target

[Andy Holcomb]

I primarily use a build accelerator like Incredibuild for larger projects. One of the inefficiencies I've run into is when developers initiate a remote build on a project that is not "dirty". We invoke the build accelerator which has to connect to a remote node, sync the filesystem, and invoke ninja which (correctly) returns "no work to do". While this happens in only a couple seconds, it is wasteful and inefficient.

It would be nice to have a subtool that I can run to return whether or not the target actually needs to be built. This way I can check the status of the target before invoking the build accelerator.

I've tried using the 'dry-run' mode, but it doesn't actually return "no work to do" when I would expect it to.

Any thoughts would be appreciated. Thanks!

Andy