Add a new key to a Step, named Artifacts. If present, it indicates that
the step has a "default" Kind and Container that can be easily retrieved
without explicitly specifying either when producing an artifact.
EarlyFunctionAnalysis now can be invoked to schedule a full
ABI analysis over the collected functions via `--detect-abi`
option, or it can limit itself to simply recover the CFG and
serialize it onto the LLVM IR via `--collect-cfg` option.
Giacomo Vercesi