Auto merge of #7390 - Eh2406:better-graph, r=alexcrichton
Auto merge of #7390 - Eh2406:better-graph, r=alexcrichton

change the priority in witch we build crates

On my windows 4 core, this made clean builds (of 3596cb86b2e87dd9b9c1bb90d4a9d73ec2c1512f) go from 257-223s to 210-205s. So that looks like an improvement.

tsurai/cargo,tshepang/cargo,nipunn1313/cargo,tsurai/cargo,rust-lang/cargo,tsurai/cargo,tsurai/cargo,eminence/cargo,tsurai/cargo,tshepang/cargo,nipunn1313/cargo,vojtechkral/cargo,rustyhorde/cargo,vojtechkral/cargo,rustyhorde/cargo,eminence/cargo,eminence/cargo,rustyhorde/cargo,vojtechkral/cargo,rust-lang/cargo,rust-lang/cargo,nipunn1313/cargo,rustyhorde/cargo,vojtechkral/cargo,rust-lang/cargo,eminence/cargo,nipunn1313/cargo,tshepang/cargo,tshepang/cargo