In clang-interpreter example JIT (ExecutionEngine::JITCtor) is not
initialized, making program always fail with "unable to make execution
engine: JIT has not been linked in."
Adding #include "llvm/ExecutionEngine/JIT.h" to
clang-interpreter:main.cpp solves the problem (based on a comment in
llvm/ExecutionEngine/JIT.h stating "This file forces the JIT to link
in on certain operating systems (Windows))