In the new scheme, dg-do <what> is joined by dg-do <what> <style>
<slave-file-list> where <style> is one of "onestep", "multi", and
"serial", and the slaves are files that contain dg-do dummy. The
non-dg-dummy files are _master_ test files.
onestep -- src files are compiled in one step, output is a single file
multi -- same, but each file produces a single output file
serial -- same, but files are compiled individually
Rather than being completely explicit at this time, let me just say the
some sort of "environment" may pertain while the compiles are going on,
and the results, even in the 3rd case, may depend on all the input files
at once. Or not. :-)