Clang 3.6 creates a warning if the override keyword is missing. This should maybe not be interpreted as an error yet.
add
mitkFunctionCheckCAndCXXCompilerFlags("-Wno-error=inconsistent-missing-override" module_c_flags module_cxx_flags)
to
/home/christoph/data/dartclients/clang-mitk-debug/MITK/CMake/mitkFunctionCreateModule.cmake