[CMake] autoheader

[Alexander Neundorf]

On Tuesday 31 March 2009, BRM wrote:
> I think the better solution would be to have the various Find functions
> (package, library, program) define a variable for that package to an
> internal list - which is what I think Marcel might have been hinting at.

Something similar exists for FIND_PACKAGE() since 2.6.0.
Each call to FIND_PACKAGE() appends to the global properties ENABLED_FEATURES 
or DISABLED_FEATURES depending on the result (respecting the QUIET keyword).
It also appends to PACKAGES_FOUND and PACKAGES_NOT_FOUND respectively  
(always, i.e. independent from the QUIET keyword).
These properties can be used then with the macros provided in 
FeatureSummary.cmake.

Alex