[llvm] Fixed build with C++20 standard (PR #169772)

[Vedran Miletić via llvm-commits]

================
@@ -267,6 +267,8 @@ class iterator_adaptor_base
     return *static_cast<DerivedT *>(this);
   }
   using BaseT::operator-;
+  template <bool Enabled = bool(BaseT::IsRandomAccess),
+            std::enable_if_t<Enabled, int> = 0>
----------------
vedranmiletic wrote:

Agreed, much more readable.

https://github.com/llvm/llvm-project/pull/169772