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

[Vedran Miletić via llvm-commits]

================
@@ -267,7 +267,11 @@ class iterator_adaptor_base
     return *static_cast<DerivedT *>(this);
   }
   using BaseT::operator-;
-  difference_type operator-(const DerivedT &RHS) const {
+  difference_type operator-(const DerivedT &RHS) const
+#ifdef __cpp_concepts
+    requires(bool(BaseT::IsRandomAccess))
+#endif
+  {
----------------
vedranmiletic wrote:

Good idea!

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