Warnings displayed about duplicate loop labels

[lambda-fairy]

tests/tests.rs:1:1: 1:1 warning: label name `__maud_loop_label` shadows a label name that is already in scope
tests/tests.rs:1 #![feature(plugin)]
                 ^
tests/tests.rs:450:5: 450:17 note: in this expansion of html! (defined in tests/tests.rs)
tests/tests.rs:1:1: 1:1 note: shadowed label `__maud_loop_label` declared here
tests/tests.rs:1 #![feature(plugin)]
                 ^
tests/tests.rs:449:5: 449:17 note: in this expansion of html! (defined in tests/tests.rs)
tests/tests.rs:1:1: 1:1 warning: label name `__maud_loop_label` shadows a label name that is already in scope
tests/tests.rs:1 #![feature(plugin)]
                 ^
tests/tests.rs:483:5: 483:20 note: in this expansion of html! (defined in tests/tests.rs)
tests/tests.rs:1:1: 1:1 note: shadowed label `__maud_loop_label` declared here
tests/tests.rs:1 #![feature(plugin)]
                 ^
tests/tests.rs:482:5: 482:20 note: in this expansion of html! (defined in tests/tests.rs)

Probably related to rust-lang/rust#21633