Utilities for compiling and running on the reference backend with a JIT.
The runtime itself lives in {include,lib}/RefBackend/Runtime, but since it
is totally firewalled from the compiler codebase, it presents a fairly
bare-bones interface (e.g. it doesn't use libSupport, can't use LLVM's JIT
interfaces, etc.).
The interface provided in this directory uses standard LLVM conventions and
freely relies on libSupport, JIT utilities, etc.