[CMake] automatically re-generating makefiles

[Bill Hoffman]

Matthew Woehlke wrote:

>> Makefile : cmake_check_build_system
> 
> Shouldn't this rather be:
> Makefile: <list of CMakeLists.txt, etc>
>     cmake_check_build_system
> ?
> 
> ...in which case, the only thing that should get checked is if the 
> CMakeLists.txt are newer than the Makefile. So in most cases this should 
> be fast.
> 
We need to run cmake_check_build_system first because make can not 
handle missing depend .h files.   The check build system step makes sure 
the current set of depends won't kill make.   It is also useful for 
getting around some other make limitations that I can not remember right 
now.


-Bill