Fix compilation failure when using libstdc++10 (#1929)

The issue is caused by deleted `std::__detail::begin` declared in `bits/iterator_concepts.h`. This would be found by ADL, and because it is deleted, compilation would fail. This change makes it so that we SFINAE on `begin(std::declval<T>())` and `end(std::declval<T>())` being well-formed.

src/catch2/catch_tostring.hpp

@@ -446,20 +446,27 @@ namespace Catch {
 #endif // CATCH_CONFIG_ENABLE_VARIANT_STRINGMAKER
 
 namespace Catch {
-    struct not_this_one {}; // Tag type for detecting which begin/ end are being selected
+    // Import begin/ end from std here
-
-    // Import begin/ end from std here so they are considered alongside the fallback (...) overloads in this namespace
     using std::begin;
     using std::end;
 
-    not_this_one begin( ... );
+    namespace detail {
-    not_this_one end( ... );
+        template <typename...>
+        struct void_type {
+            using type = void;
+        };
+
+        template <typename T, typename = void>
+        struct is_range_impl : std::false_type {
+        };
+
+        template <typename T>
+        struct is_range_impl<T, typename void_type<decltype(begin(std::declval<T>()))>::type> : std::true_type {
+        };
+    } // namespace detail
 
     template <typename T>
-    struct is_range {
+    struct is_range : detail::is_range_impl<T> {
-        static const bool value =
-            !std::is_same<decltype(begin(std::declval<T>())), not_this_one>::value &&
-            !std::is_same<decltype(end(std::declval<T>())), not_this_one>::value;
     };
 
 #if defined(_MANAGED) // Managed types are never ranges