add turbofish to fix build error, rm duplicate feature gate

Author: IntegralPilot

library/core/src/num/int_macros.rs

@@ -3876,7 +3876,7 @@ macro_rules! int_impl {
         #[unstable(feature = "clamp_magnitude", issue = "148519")]
         #[inline]
         pub fn clamp_magnitude(self, limit: $UnsignedT) -> Self {
-            if let Ok(limit) = limit.try_into() {
+            if let Ok(limit) = limit.try_into::<$SelfT>() {
                 self.clamp(-limit, limit)
             } else {
                 self

library/coretests/tests/num/clamp_magnitude.rs

@@ -1,5 +1,3 @@
-#![feature(clamp_magnitude)]
-
 macro_rules! check_int_clamp {
     ($t:ty, $ut:ty) => {
         let min = <$t>::MIN;