[llvm] [llvm] replace static_assert with std::enable_if_t in ilist_node_impl (PR #127722)

[Andrew Rogers via llvm-commits]

================
@@ -147,9 +149,8 @@ class ilist_node_impl
   ///
   /// This requires sentinel tracking to be explicitly enabled.  Use the
   /// ilist_sentinel_tracking<true> option to get this API.
-  bool isSentinel() const {
-    static_assert(OptionsT::is_sentinel_tracking_explicit,
-                  "Use ilist_sentinel_tracking<true> to enable isSentinel()");
+  template <typename T = OptionsT>
+  std::enable_if_t<T::is_sentinel_tracking_explicit, bool> isSentinel() const {
----------------
andrurogerz wrote:

To clarify: are you asking for a comment explaining why `std::enable_if_t` is on the return value instead of how I had it before?

https://github.com/llvm/llvm-project/pull/127722