core_arch: Add LoongArch LSX testcases

library/stdarch/crates/core_arch/src/loongarch64/lsx/mod.rs

@@ -11,3 +11,7 @@ mod generated;
 #[rustfmt::skip]
 #[unstable(feature = "stdarch_loongarch", issue = "117427")]
 pub use self::generated::*;
+
+#[rustfmt::skip]
+#[cfg(test)]
+mod tests;

library/stdarch/crates/simd-test-macro/src/lib.rs

@@ -78,6 +78,7 @@ pub fn simd_test(
             force_test = true;
             "is_mips64_feature_detected"
         }
+        "loongarch64" => "is_loongarch_feature_detected",
         t => panic!("unknown target: {t}"),
     };
     let macro_test = Ident::new(macro_test, Span::call_site());