Fix warning

Author: Kobzol

library/std_detect/tests/cpu-detection.rs

@@ -27,6 +27,16 @@
     ),
     macro_use
 )]
+#[cfg(any(
+    target_arch = "arm",
+    target_arch = "aarch64",
+    target_arch = "arm64ec",
+    target_arch = "riscv32",
+    target_arch = "riscv64",
+    target_arch = "powerpc",
+    target_arch = "powerpc64",
+    target_arch = "s390x",
+))]
 extern crate std_detect;
 
 #[test]