[m-rev.] for review: Parallelise make_java_csharp_arena_{base, diff}

[Zoltan Somogyi]

On Thu, 26 Jul 2018 10:40:33 +1000, Peter Wang <novalazy at gmail.com> wrote:
> +# The environment variable PARALLEL controls the maximum number of compiler
> +# processes to run at a time.

I would have made the env var name something more specific to this script,
such as JC_PARALLEL, to reduce the chances of collision with other software.
  
> +PARALLEL=${PARALLEL:-`nproc 2>/dev/null`}

On my laptop, nproc prints 8, even though it has only 4 cores,
because the cores have hyperthreading. It would be nice
if there were a way of disregarding hyperthreading,
but nproc does not seem to have to do that.

Given that users can set the value themselves, this is not a real problem.

Both of the above concerns are about "would be nice to have"s.
The diff is fine as it is.

Zoltan.