re-export is_loongarch_feature_detected

Author: heiher

Diff for: library/std/src/lib.rs

@@ -660,6 +660,8 @@ pub mod arch {
     pub use std_detect::is_arm_feature_detected;
     #[unstable(feature = "is_riscv_feature_detected", issue = "111192")]
     pub use std_detect::is_riscv_feature_detected;
+    #[unstable(feature = "is_loongarch_feature_detected", issue = "117425")]
+    pub use std_detect::is_loongarch_feature_detected;
     #[stable(feature = "simd_x86", since = "1.27.0")]
     pub use std_detect::is_x86_feature_detected;
     #[unstable(feature = "stdarch_mips_feature_detection", issue = "111188")]