CMake cache not deleted on build.sh -c, causes linker errors

[apsabelhaus]

We need to have the build script delete the CMake cache, under build/CMakeFiles and build/CMakeCache.txt, when make clean is run. (That's ./build.sh -c)

I've been getting annoying linker errors when pulling from branches where CMake assumes files are linked one way, but they're done differently in different branches. Errors appear in particular with dev/dhustigschultz/BP_SC_NoLegs_Stats, and related.

Errors are fixed by deleting the cache under the build/ directory (files listed above), or the whole build/ directory itself.