Auto merge of #5118 - Eh2406:more_rc, r=alexcrichton
authorbors <bors@rust-lang.org>
Sun, 4 Mar 2018 20:47:56 +0000 (20:47 +0000)
committerbors <bors@rust-lang.org>
Sun, 4 Mar 2018 20:47:56 +0000 (20:47 +0000)
use more Rc in the part of resolver that gets cloned a lot

In a test on https://github.com/rust-lang/cargo/issues/4810#issuecomment-357553286
Before we got to 1700000 ticks in ~(82 to 97) sec
After we got to 1700000 ticks in ~(63 to 67) sec


Trivial merge