[CMake] build time / unneccessary configure for library targets on switch from 2.0.6 to 2.4.2

[Brad King]

Jan Woetzel wrote:
> In particular when nothing has changed the "nothing to do" build now 
> takes >> 60 seconds.
> With 2.06 it took < 5 seconds as expected to build when everything was 
> up to date.
> 
> The problem seems to be:
> Although nothing has changed
> cmake configures, generates and writes toplevel build files
> for every library target on each build.
> I expected it only on teh first cmake run or if any of the files (e.g. 
> CmakeListst.txt) changed.
> This consumes a lot of time.

CMake generates rules to automatically regenerate the project when 
CMakeLists.txt code changes (2.0 did also).  For some reason Visual 
Studio is deciding to run these rules probably because it thinks the 
CMake input files have changed.  You'll have to check file modification 
times.  Look for a file with a date in the future in the source tree.

-Brad