An undefined atomic operation function was declared.
Erroneous code example:
```compile_fail,E0092
#![feature(intrinsics)]
extern "rust-intrinsic" {
fn atomic_foo(); // error: unrecognized atomic operation
// function
}
```
Please check you didn't make a mistake in the function's name. All intrinsic
functions are defined in `librustc_codegen_llvm/intrinsic.rs` and in
`libcore/intrinsics.rs` in the Rust source code. Example:
```
#![feature(intrinsics)]
extern "rust-intrinsic" {
fn atomic_fence(); // ok!
}
```