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

[Saleem Abdulrasool via llvm-commits]

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@@ -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 {
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compnerd wrote:

@kuhar I don't think that it can be removed ever due to the `static_assert` being used to prevent the use of the function. If the method is instantiated, the `static_assert` will be evaluated. However, when building LLVM as a DLL, the method will be instantiated by default as per the behaviour of DLLExport on Windows. So, that would require that we default to explicit sentinel tracking which is an optional debugging aide.

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