Auto merge of rust-lang#7253 - flip1995:shrink-monster, r=xFrednet

Early return from LintPass registration when collecting metadata

This speeds up the metadata collection by 2-2.5x on my machine. During
metadata collection other lint passes don't have to be registered, only
the lints themselves.

cc rust-lang#7172

r? `@xFrednet`

changelog: none

Author: bors