[CMake] Generate a file with a custom command as part of build

[Michael Ellery]

> On Jan 24, 2017, at 11:22 PM, doug livesey <biot023 at gmail.com> wrote:
> 
> Is there any way that I can make the files webpack compiles into dependencies for the Webpack task? So that any changes to those are picked up for recompilation?
> No worries if not, I just thought it would be nice.
> 

just add any files on which the command depends after the DEPENDS argument. I only added the one source file in that example, but you can add as many as are appropriate.

-Mike