Rollup merge of #114496 - taiki-e:sparc32-atomic, r=Amanieu

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. taiki-e/rust-cross-toolchain@02efe1e)

r? `@Amanieu`

Author: matthiaskrgr