* Add ability to run CLIF IR using `clif-util run [-v] {file}` and add `test run` to cranelift-filetests to allow executing CLIF
This re-factors the compile/execute parts to a FunctionRunner that is shared between cranelift-filetests and clif-util. CLIF can be now be run using `clif-util run` as well as during `clif-util test` for files with a `test run` header. As before, only functions suffixed with a `run` comment are executed. The `run: fn(...) == ...` expression syntax is left for a subsequent change.
