Can't create new projects with Clang 4.0

I managed to get 4.15.2 to compile and run successfully with Clang 4.0. The only issue is I keep getting the error message:

No compiler was found. In order to use C++ template, you must first install an IDE to edit source code.

Which file do I need to look at editing to get Unreal to notice Clang 4.0 is supported when creating a new project?

You need to change FNullSourceCodeAccessor::CanAccessSourceCode() in NullSourceCodeAccessor.cpp.