option(STL_DEBUG "Enable STL debug checks. Warning: This must be consistent across the whole build! Not compatible with the libc++ shipped with Apple XCode as of 2019." OFF)
if(STL_DEBUG)
# We do not know which STL will be used, defining both is the easist way.
message(SEND_ERROR "Building in the source directory is not supported.")
message(FATAL_ERROR "Please remove the created \"CMakeCache.txt\" file, the \"CMakeFiles\" directory and create a build directory and call \"${CMAKE_COMMAND} <path to the sources>\".")