Supress unused_macros error on architectures with no atomics.
Supress unused_macros error on architectures with no atomics.

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