dev-lang/rust does not respect MAKEOPTS from make.conf during bootstrap

[stefson]

This is a problem if the build system does not have much ram per thread, or not much in general, or for a possible debug build. I did a bit of research, pullrequest #95 does have the results. For dev-util/cargo the problem has been solved, for dev-lang/rust it has been mitigated by a lot in restricting ./x.py

What is left to be dealt with is the minimal bootstrap between src_configure and the execution of ./x.py ; did a reasonable amount of research about what is going on there, but found nothing helpfull in terms of restricting the jobs, or even make them honor the MAKEOPTS from make.conf

Therefore, I think it should be okay to commit the pullrequest to the overlay, and to pick up the rest of the problem later on.

[stefson]

I'll take with upstream about this.

[blueness]

ok