[CMake] Generator-independent incremental CMake run

[David Cole]

> We have a fairly large project with about 400 targets.
>   $ cmake %builddir%
>   -> takes about 5 minutes for a No-op
>
>   $ cmake --build %builddir% --target ZERO_CHECK
>   -> takes 20 seconds for No-op

This is the problem.

"cmake %builddir%" should be as fast as possible for a no-op... If it's 
not, it would be good to solve the real underlying problem that causes 
it to take 5 minutes for "nothing" rather than write elaborate scripts 
to try to workaround it.

Is your project publicly available so CMake devs can try to figure out 
why it takes so long?

Or... can you produce a generated repro case that demonstrates a long 
no-op time....?

There must be something in your project's CMake code that triggers the 
performance problem.

Does it still happen with the latest release (CMake 3.0.1)?


D