Expose tests for {f32,f64}.total_cmp in docs, along with comment

Reformat so the helpful assert_eq! line, which is stripped out
completely in docs due to being commented out.

Apparently, according to discussion, the result may differ on other
architectures or LLVM versions, so show the two potential results.

library/core/src/num/f32.rs

@@ -1424,9 +1424,19 @@ impl f32 {
     /// ];
     ///
     /// bois.sort_by(|a, b| a.weight.total_cmp(&b.weight));
-    /// # assert!(bois.into_iter().map(|b| b.weight)
-    /// #     .zip([-5.0, 0.1, 10.0, 99.0, f32::INFINITY, f32::NAN].iter())
-    /// #     .all(|(a, b)| a.to_bits() == b.to_bits()))
+    /// ```
+    /// Since the NaN constant does not have a well-defined sign,
+    /// this test may result in either:
+    /// ```
+    /// assert!(bois.into_iter().map(|b| b.weight)
+    ///     .zip([-5.0, 0.1, 10.0, 99.0, f32::INFINITY, f32::NAN].iter())
+    ///     .all(|(a, b)| a.to_bits() == b.to_bits()))
+    /// ```
+    /// or:
+    /// ```
+    /// assert!(bois.into_iter().map(|b| b.weight)
+    ///     .zip([f32::NAN, -5.0, 0.1, 10.0, 99.0, f32::INFINITY].iter())
+    ///     .all(|(a, b)| a.to_bits() == b.to_bits()))
     /// ```
     #[stable(feature = "total_cmp", since = "1.62.0")]
     #[must_use]

library/core/src/num/f64.rs

@@ -1422,9 +1422,19 @@ impl f64 {
     /// ];
     ///
     /// bois.sort_by(|a, b| a.weight.total_cmp(&b.weight));
-    /// # assert!(bois.into_iter().map(|b| b.weight)
-    /// #     .zip([-5.0, 0.1, 10.0, 99.0, f64::INFINITY, f64::NAN].iter())
-    /// #     .all(|(a, b)| a.to_bits() == b.to_bits()))
+    /// ```
+    /// Since the NaN constant does not have a well-defined sign,
+    /// this test may result in either:
+    /// ```
+    /// assert!(bois.into_iter().map(|b| b.weight)
+    ///     .zip([-5.0, 0.1, 10.0, 99.0, f64::INFINITY, f64::NAN].iter())
+    ///     .all(|(a, b)| a.to_bits() == b.to_bits()))
+    /// ```
+    /// or:
+    /// ```
+    /// assert!(bois.into_iter().map(|b| b.weight)
+    ///     .zip([f64::NAN, -5.0, 0.1, 10.0, 99.0, f64::INFINITY].iter())
+    ///     .all(|(a, b)| a.to_bits() == b.to_bits()))
     /// ```
     #[stable(feature = "total_cmp", since = "1.62.0")]
     #[must_use]