[CMake] FILE command in make_custom_target

[Bill Hoffman]

Philippe Fremy wrote:
>
> It is ironic that a running cmake instance, that supports platform
> agnostic directory creation, is not able to do that inside a rule and
> has to fallback an calling a second cmake instance for that.
>
>   
Actually, when a custom command is run, there is no running cmake 
instance.  That is run
during build time, and at that point cmake is no longer running, make, 
or some IDE is running.

-Bill