Builds are completely serialized on Windows

[jakepetroules]

This is a regression introduced by #597, where the following line 3900ed4#diff-bd65cf12ed29b52c530ff04d2c678eb66883eddfcb44d5dbb8fe499f25865e93R219 presumably meant to use std::max instead of std::min.

The impact of this is that estimateTaskLimits falls back to a default case of returning only a single lane, regardless of the number of requested lanes, and consequently all builds are serialized.