Fix pool::Arc being enabled without atomics.

CHANGELOG.md

@@ -98,6 +98,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Fixed
 
+- Fixed compilation on `thumbv6m-none-eabi` without `portable-atomic` feature.
 - Fixed clippy lints.
 - Fixed `{arc,box,object}_pool!` emitting clippy lints.
 - Fixed the list of implemented data structures in the crate docs, by adding `Deque`,

build.rs

@@ -1,5 +1,3 @@
-#![deny(warnings)]
-
 use std::{
     env,
     error::Error,

src/pool.rs

@@ -54,6 +54,7 @@
 
 mod treiber;
 
+#[cfg(any(feature = "portable-atomic", target_has_atomic = "ptr"))]
 pub mod arc;
 pub mod boxed;
 pub mod object;

tests/tsan.rs

@@ -1,6 +1,5 @@
 #![deny(rust_2018_compatibility)]
 #![deny(rust_2018_idioms)]
-#![deny(warnings)]
 
 use std::{ptr::addr_of_mut, thread};