Replace usages of 'bad_style' with 'nonstandard_style'.

`bad_style` is being deprecated in favor of `nonstandard_style`:

- https://github.com/rust-lang/rust/issues/41646

src/test/run-pass/simd-target-feature-mixup.rs

@@ -52,7 +52,7 @@ fn is_sigill(status: ExitStatus) -> bool {
 }
 
 #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
-#[allow(bad_style)]
+#[allow(nonstandard_style)]
 mod test {
     // An SSE type
     #[repr(simd)]