[flang] Cope with specific procedures with same name as generic

[klausler]

Summary

When accessing a specific procedure of a USE-associated generic
interface, we need to allow for the case in which that specific
procedure has the same name as the generic when testing for
its availability in the current scope.

flang/lib/Semantics/expression.cpp

   } else if (const auto *used{
                  originalGeneric.detailsIf<semantics::UseDetails>()}) {
     const auto &scope{originalGeneric.owner()};
-    auto iter{scope.find(specific.name())};
-    if (iter != scope.end() && iter->second->has<semantics::UseDetails>() &&
-        &iter->second->get<semantics::UseDetails>().symbol() == &specific) {
-      return specific;
-    } else {
-      // Create a renaming USE of the specific procedure.
-      auto rename{context_.SaveTempName(
-          used->symbol().owner().GetName().value().ToString() + "$" +
-          specific.name().ToString())};
-      return *const_cast<semantics::Scope &>(scope)
-                  .try_emplace(rename, specific.attrs(),
-                      semantics::UseDetails{rename, specific})
-                  .first->second;
+    if (auto iter{scope.find(specific.name())}; iter != scope.end()) {
+      if (const auto *useDetails{
+              iter->second->detailsIf<semantics::UseDetails>()}) {
+        const Symbol &usedSymbol{useDetails->symbol()};
+        const auto *usedGeneric{
+            usedSymbol.detailsIf<semantics::GenericDetails>()};
+        if (&usedSymbol == &specific ||
+            (usedGeneric && usedGeneric->specific() == &specific)) {
+          return specific;
+        }
+      }
     }
+    // Create a renaming USE of the specific procedure.
+    auto rename{context_.SaveTempName(
+        used->symbol().owner().GetName().value().ToString() + "$" +
+        specific.name().ToString())};
+    return *const_cast<semantics::Scope &>(scope)
+                .try_emplace(rename, specific.attrs(),
+                    semantics::UseDetails{rename, specific})
+                .first->second;
   } else {
     return specific;
   }