[CMake] Specifying a pre-build dependency?

[Bryan O'Sullivan]

David Cole wrote:
> When is "on demand"?
> 
> You could do this at CMake configure time if the "on demand" choice is 
> based on something known at CMake configure time.

That might do the trick.

Essentially, I'd like to be able to shove prebuilt object files and 
headers for a third party library into a zip file per architecture, and 
have the appropriate zeip file downloaded and unpacked early enough that 
the header files are actually findable by the compiler by the time I 
start compiling source files in my tree.

The one wrinkle is that I'd ideally like to have separate bundles for 
debug and optimised versions of these libraries to keep download sizes 
small (most people will never fetch the debug libraries), and that level 
of knowledge isn't AFAIK available at configure time.

	<b