[llvm] [ADT] Make `is_scoped_enum_v` SFINAE-able (PR #138134)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-adt

Author: Vlad Serebrennikov (Endilll)

<details>
<summary>Changes</summary>

...in old compilers where `std::underlying_type` is not SFINAE-friendly. Fixes buildbot failure https://lab.llvm.org/buildbot/#/builders/134/builds/17904 caused by #<!-- -->138089. Demo: https://godbolt.org/z/1dj5Ysn8E

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Full diff: https://github.com/llvm/llvm-project/pull/138134.diff


1 Files Affected:

- (modified) llvm/include/llvm/ADT/STLForwardCompat.h (+2-1) 


``````````diff
diff --git a/llvm/include/llvm/ADT/STLForwardCompat.h b/llvm/include/llvm/ADT/STLForwardCompat.h
index b8d4babc95fea..c70f4dc29aee0 100644
--- a/llvm/include/llvm/ADT/STLForwardCompat.h
+++ b/llvm/include/llvm/ADT/STLForwardCompat.h
@@ -73,7 +73,8 @@ struct from_range_t {
 };
 inline constexpr from_range_t from_range{};
 
-template <typename T, typename UnderlyingT = std::underlying_type_t<T>>
+template <typename T, typename UnderlyingT = typename std::enable_if_t<
+                          std::is_enum_v<T>, std::underlying_type<T>>::type>
 constexpr bool is_scoped_enum_v =
     std::is_enum_v<T> && !std::is_convertible_v<T, UnderlyingT>;
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/138134