Re-add comment about behaviour of inline.

src/libcore/num/mod.rs

@@ -2001,6 +2001,9 @@ $EndFeature, "
             #[inline]
             #[rustc_inherit_overflow_checks]
             pub const fn abs(self) -> Self {
+                // Note that the #[inline] above means that the overflow
+                // semantics of the subtraction depend on the crate we're being
+                // inlined into.
                 if self.is_negative() {
                     -self
                 } else {