decl_macro and use std::vec combo breaks rustdoc

[MaloJaffre]

A crate with the following reduced lib.rs breaks rustdoc:

#![feature(decl_macro)]
use std::vec;

Indeed, rustdoc links to vec!() docs in index.html because this macro has the same name than the imported module (???).

Furthermore, the macro page linked has broken links because it is copied in the crate namespace, instead of being directly https://doc.rust-lang.org/std/vec/struct.Vec.html.

rustc 1.24.0-nightly (cddc4a62d 2017-12-26)
binary: rustc
commit-hash: cddc4a62d8e72c2bd303994752a7f8545ffb9c79
commit-date: 2017-12-26
host: x86_64-unknown-linux-gnu
release: 1.24.0-nightly
LLVM version: 4.0