[flang] Ignore BIND(C) binding name conflicts of inner procedures

[klausler]

Summary

The binding names of inner procedures with BIND(C) are not exposed
to the loader and should be ignored for potential conflict errors.

flang/lib/Semantics/check-declarations.cpp

if (ultimate.has<DerivedTypeDetails>()) {
       }
     }
   }
   helper.Check(scope);
 }
 
 static const std::string *DefinesBindCName(const Symbol &symbol) {
   const auto *subp{symbol.detailsIf<SubprogramDetails>()};
-  if ((subp && !subp->isInterface()) || symbol.has<ObjectEntityDetails>()) {
+  if ((subp && !subp->isInterface() &&
+          ClassifyProcedure(symbol) != ProcedureDefinitionClass::Internal) ||
+      symbol.has<ObjectEntityDetails>()) {
     // Symbol defines data or entry point
     return symbol.GetBindName();
   } else {
     return nullptr;
   }
 }
 
 // Check that BIND(C) names are distinct