llvm-xray extract <object file> [-o <filename or '-'>]
The tool gets the XRay instrumentation map from an object file and turns
it into YAML. We first support ELF64 sleds on x86_64 binaries, with
provision for supporting other supported platforms and formats later.
This is the first of a many-part change to fully implement the
We also define a subcommand registration and dispatch mechanism to be
used by other further subcommand implementations for llvm-xray.