[request] Use libconfsyscpus to correctly report 2 CPUs

[rtfeldman]

We've been experiencing radically slow Elm builds on Travis - as in, 4 minutes instead of 4 seconds - which turned out to be because sysconf misreports the number of CPUs as more than the 2 that the instance actually has access to.

libsysconfcpus lets you adjust the number of CPUs that sysconf reports, so presumably it could be used on the instances to have them report accurate core counts. This would help not only Elm tests but any other tests that run in parallel.

We confirmed that adjusting what sysconf reports like this fixes the problem; it makes the Elm tests drop from several minutes to several seconds.

Using libsysconf to address this would also address the CPU portion of #4696 by enabling people to use normal sysconf to obtain an accurate core count.

[stale]

Thanks for contributing to this issue. As it has been 90 days since the last activity, we are automatically closing the issue. This is often because the request was already solved in some way and it just wasn't updated or it's no longer applicable. If that's not the case, please do feel free to either reopen this issue or open a new one. We'll gladly take a look again! You can read more here: https://blog.travis-ci.com/2018-03-09-closing-old-issues