[CMake] ExternalProject and redundant update/configure/compile actions.

[David Cole]

> ... then the project never rebuilds, since reconfigure and rebuild 
depend on update.
> So if you modify a source file of a project without a download 
command, then
> superbuild will not rebuild the project.


Ahem. "If you modify a source file of a project" then *you* should 
rebuild the project.

ExternalProject does not now and never will handle inter-project 
source-level dependencies properly (with minimal rebuilds). That's what 
add_subdirectory and "interal projects" are all about.

You can try to make EP do what you want, but .... if you are modifying 
these things then they are NOT really "External."

You can "Square peg. Round hole. Make it fit with brute force CMake 
code anyway." as much as you want.

But I wouldn't do that.


;-)
D