[flang] Silence warnings from hermetic module files (llvm#128763)

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

@@ -1546,6 +1546,10 @@ 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);