CMake profiling results

[hkaiser]

CMake V3.18 can output profiling traces. The results show that about 40% of the time is spent in configuring and about 60% of the time is spent generating the make files. The interesting part is that during generation, about 50% of the time is spent in the function create_configarion_summary, and about 20-30% are spent during generating the force_linking header and source files (will go away soon). Here is an exemplar visualization for one of the HPX modules:

that demonstrates this nicely. I think we may have some low-hanging fruit here allowing to significantly reducing the generation phase of our build system.