ActsTrackReconstruction: Fix warning in LTO build.

The tests in this package use #undef NDEBUG to enable assertions in all builds. However, they also link directly with source files from the library. (Can't link directly against the library because only a component library is built.)

However, the code from the library also needs to be compiled with -UNDEBUG. Otherwise we get warnings in the LTO build because inlined code in TrkEventPrimitives/TrkObjectCounter.h changes behavior based on whether or not NDEBUG is defined.

Work around by simply #including the library code into the tests rather than compiling it separately.