add missing safety comments

Author: RalfJung

library/core/src/num/f128.rs

@@ -1378,6 +1378,7 @@ impl f128 {
 #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
 #[must_use = "method returns a new number and does not mutate the original value"]
 pubconstfncopysign(self,sign:f128) -> f128{
+// SAFETY: this is actually a safe intrinsic
 unsafe{ intrinsics::copysignf128(self, sign)}
 }
 }

library/core/src/num/f16.rs

@@ -1352,6 +1352,7 @@ impl f16 {
 #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
 #[must_use = "method returns a new number and does not mutate the original value"]
 pubconstfncopysign(self,sign:f16) -> f16{
+// SAFETY: this is actually a safe intrinsic
 unsafe{ intrinsics::copysignf16(self, sign)}
 }
 }

library/core/src/num/f32.rs

@@ -1449,6 +1449,7 @@ impl f32 {
 #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
 #[inline]
 pubconstfnabs(self) -> f32{
+// SAFETY: this is actually a safe intrinsic
 unsafe{ intrinsics::fabsf32(self)}
 }
 
@@ -1509,6 +1510,7 @@ impl f32 {
 #[stable(feature = "copysign", since = "1.35.0")]
 #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
 pubconstfncopysign(self,sign:f32) -> f32{
+// SAFETY: this is actually a safe intrinsic
 unsafe{ intrinsics::copysignf32(self, sign)}
 }
 }

library/core/src/num/f64.rs

@@ -1449,6 +1449,7 @@ impl f64 {
 #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
 #[inline]
 pubconstfnabs(self) -> f64{
+// SAFETY: this is actually a safe intrinsic
 unsafe{ intrinsics::fabsf64(self)}
 }
 
@@ -1509,6 +1510,7 @@ impl f64 {
 #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
 #[inline]
 pubconstfncopysign(self,sign:f64) -> f64{
+// SAFETY: this is actually a safe intrinsic
 unsafe{ intrinsics::copysignf64(self, sign)}
 }
 }