Set max_atomic_width to match risc0 value

Not entirely sure yet what we want this to be set to

Author: lrettig

patches/rust.patch

@@ -31,7 +31,7 @@ index 000000000..7a09c78a4
 +            cpu: "generic-rv32".into(),
 +            features: "+e,+m".into(),
 +            llvm_abiname: "ilp32e".into(),
-+            max_atomic_width: Some(32),
++            max_atomic_width: Some(64),
 +            os: "zkvm".into(),
 +            vendor: "athena".into(),
 +            singlethread: true,