hack signum as well

library/core/src/num/int_macros.rs

@@ -2603,13 +2603,16 @@ pub const fn abs_diff(self, other: Self) -> $UnsignedT {
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline(always)]
-        #[rustc_allow_const_fn_unstable(const_cmp)]
         pub const fn signum(self) -> Self {
             // Picking the right way to phrase this is complicated
             // (<https://graphics.stanford.edu/~seander/bithacks.html#CopyIntegerSign>)
             // so delegate it to `Ord` which is already producing -1/0/+1
             // exactly like we need and can be the place to deal with the complexity.
-            self.cmp(&0) as _
+
+            // FIXME(const-hack): replace with cmp
+            if self < 0 { -1 }
+            else if self == 0 { 0 }
+            else { 1 }
         }
 
         /// Returns `true` if `self` is positive and `false` if the number is zero or