[VecOps] Fix ROOT-9669: value printing of RVec<T> where T does not have an operator<<

this has been resolved relying on value printing itself for the individual items.

math/vecops/inc/ROOT/RVec.hxx

@@ -1060,11 +1060,23 @@ TVEC_EXTERN_VDT_UNARY_FUNCTION(double, fast_atan)
 
 namespace cling {
 template <typename T>
-inline std::string printValue(ROOT::VecOps::RVec<T> *tvec)
+inline std::string printValue(ROOT::VecOps::RVec<T> *rvecp)
 {
-   std::stringstream ss;
-   ss << *tvec;
-   return ss.str();
+   std::stringstream os;
+
+   auto &rvec = *rvecp;
+
+   os << "{ ";
+   const auto size = rvec.size();
+   if (size) {
+      for (std::size_t i = 0; i < size - 1; ++i) {
+         os << printValue(&(rvec[i])) << ", ";
+      }
+      os << printValue(&(rvec[size - 1]));
+   }
+   os << " }";
+
+   return os.str();
 }
 
 } // namespace cling