Parallel builds don't work: Cabal (library) bug on configure?

[snoyberg]

When I have parallel builds on, the runhaskell Setup.hs build steps will sporadically fail about "need to configure", but if I set the number of Shake flags to 1, it works. We may want to conditionally set threads to 1 on Windows for an initial release, and then debug what's happening.

[snoyberg]

Initial hack done, deferring to later milestone.

[snoyberg]

This now appears to be occurring on Linux as well

[snoyberg]

I suspect that this is a bug in the Cabal library. However, b511d70 introduces a resilient workaround. I'm going to move this to a later milestone for now, but may end up closing it completely.