[flang] Silence warnings from hermetic module files

Modules read from module files must have their symbols tagged with
the ModFile flag to suppress all warnings messages that might be
emitted for their contents.  (Actionable warnings will have been
emitted when the modules were originally compiled, so we don't want
to repeat them later when the modules are USE'd.)  The module symbols
of the additional modules in hermetic module files were not being
tagged with that flag; fix.

Author: klausler

flang/lib/Semantics/mod-file.cpp

@@ -1563,6 +1563,10 @@ Scope *ModFileReader::Read(SourceName name, std::optional<bool> isIntrinsic,
     Scope &hermeticScope{topScope.MakeScope(Scope::Kind::Global)};
     context_.set_currentHermeticModuleFileScope(&hermeticScope);
     ResolveNames(context_, hermeticModules, hermeticScope);
+    for (auto &[_, ref] : hermeticScope) {
+      CHECK(ref->has<ModuleDetails>());
+      ref->set(Symbol::Flag::ModFile);
+    }
   }
   GetModuleDependences(context_.moduleDependences(), sourceFile->content());
   ResolveNames(context_, parseTree, topScope);