Fix CMake build/tests

[Flamefire]

I tried creating and running a CMake build via the build/CMakeLists.txt and also by adding an include_subdirectory(test) to the root CMakeLists.txt and both are not able to build the project.

I would strongly suggest to remove the build/CMakeLists.txt and have only a single (the root) file to build the library. As part of the overall effort to add CMake support to Boost, the test/CMakeLists.txt can then focus on defining tests and make use of the `BoostTest Module instead of trying to come up with a custom solution.

My WIP branch is at https://github.com/Flamefire/test/tree/cmake Currently I tried to support both CMakeLists but that is not feasible.