[llvm] r193279 - [lit] Use multiprocessing based parallelism by default, on Unix.

[Rafael Espíndola]

>      group.add_option("", "--use-processes", dest="useProcesses",
>                        help="Run tests in parallel with processes (not threads)",
> -                      action="store_true", default=False)
> +                      action="store_true", default=useProcessesIsDefault)
>      group.add_option("", "--use-threads", dest="useProcesses",
>                        help="Run tests in parallel with threads (not processes)",
> -                      action="store_false", default=False)
> +                      action="store_false", default=not useProcessesIsDefault)
>      parser.add_option_group(group)

Having two options pointing to the same variable with different
defaults is odd. I was still getting multitherading on linux. I fixed
this in r193282 and multiprocessing is now being used by default.

Cheers,
Rafael