Tidy up subtool logic #32

Some tools, e.g Eigen, Manual, have multiple "subtools", e.g. *-Split or *-Vector configurations.
There is much grotty logic e.g. in run-all:

  if ($objective.contains("Eigen")) { $out_name = "$($this.name.ToLower())_eigen" }
  elseif ($objective.contains("Light")) { $out_name = "$($this.name.ToLower())_light" }
  elseif ($objective.endswith("SPLIT")) { $out_name = "$($this.name)_split" }
  else { $out_name = $this.name }

which should be cleaned up. It's probably best for each tool's cmake script to emit to cmake-vars-$buildtype (see comments in run-all.ps1) the list of EXEs it has created, and then to uniformly name benchmarks by the name of the EXE.