This adds a global fixture that can parse an additional argument to
the test executables (`--generate_ctest_config`). When run by
CMake during build, this generates a CTest script containing all
the tests and their properties.
An additional decorator, that defines CTest properties for a test case
or suite that will be added to the tests during config generation.
This version needs no hacks, no huge CMake scripts, just a bit of
additional C++ code that iterates over all test-cases and collects
the information CTest needs.
One caveat is still that this does not work with cross-compilation,
which probably isn't an issue to begin with, but there are also ways
to fix that if necessary.
