Rollup merge of #69877 - CAD97:patch-1, r=dtolnay
Rollup merge of #69877 - CAD97:patch-1, r=dtolnay

Vec::new is const stable in 1.39 not 1.32

Changelog: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1390-2019-11-07

This really surprised me when a MSRV check for 1.35 failed with `Vec::new is not yet stable as a const fn` and the docs said that it was const stabilized in 1.32.

graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust