additional TO_NATIVE handlers, support c++ compilation for llvm, use node for ffi unwrap operation, convert scalars to vectors at native boundary, use proper nodes for interop messages

The makefiles for this project don't support running with multiple jobs
(-j ...). This tells mx not to try to use `-j`.
Also the `native` attribute is a boolean.

Refactor ffi impls into com.oracle.truffle.r.ffi.impl project; add ffi AP; TruffleLLVM all RFFI interfaces implemented; no JNI