Set max_atomic_width for sparc-unknown-linux-gnu to 32 This is currently set to 64 https://github.com/rust-lang/rust/blob/90f0b24ad3e7fc0dc0e419c9da30d74629cd5736/compiler/rustc_target/src/spec/sparc_unknown_linux_gnu.rs#L8 However, AFAIK, this architecture doesn't support 64-bit atomics, and LLVM generates libcalls: https://godbolt.org/z/chzThWGG1 (Currently, attempts to run `cargo test` for this target result in "undefined reference to `__sync_val_compare_and_swap_8'" error. https://github.com/taiki-e/rust-cross-toolchain/commit/02efe1e74f2280f06662eaf275690883b2f9c7ae) r? `@Amanieu`