[flang] Don't emit portability warnings for things in module files

[klausler]

Summary

Any symbol in a module file will have been already shamed with
portability warnings when the module was compiled, so don't pile
on when compiling other program units that use the module.
This also silences warnings about some symbols whose names were
created or extended by the compiler to avoid clashes.

[clementval]

LGTM

flang/lib/Semantics/check-declarations.cpp

 }
 
 void CheckHelper::Check(const Symbol &symbol) {
-  if (symbol.name().size() > common::maxNameLen) {
+  if (symbol.name().size() > common::maxNameLen &&
+      &symbol == &symbol.GetUltimate() &&
+      !FindModuleFileContaining(symbol.owner())) {
     messages_.Say(symbol.name(),
         "%s has length %d, which is greater than the maximum name length "
         "%d"_port_en_US,

       messages_.Say("A dummy argument must not be initialized"_err_en_US);
     } else if (IsFunctionResult(symbol)) {
       messages_.Say("A function result must not be initialized"_err_en_US);
-    } else if (IsInBlankCommon(symbol)) {
+    } else if (IsInBlankCommon(symbol) &&
+        !FindModuleFileContaining(symbol.owner())) {
       messages_.Say(
           "A variable in blank COMMON should not be initialized"_port_en_US);
     }

         }
       }
     }
-    if (derived->componentNames().empty()) { // C1805
+    if (derived->componentNames().empty() &&
+        !FindModuleFileContaining(symbol.owner())) { // C1805
       messages_.Say(symbol.name(),
           "A derived type with the BIND attribute is empty"_port_en_US);
     }

flang/lib/Semantics/resolve-names-utils.cpp

       }
     }
   }
-  if (msg) {
+  if (msg &&
+      (!context_.IsInModuleFile(source) ||
+          msg->severity() == parser::Severity::Error)) {
     context_.Say(source, std::move(*msg), sym1.name(), sym2.name());
     return false;
   }

flang/lib/Semantics/resolve-names.cpp

     }
   }
 
+  bool InModuleFile() const { return GetFoldingContext().inModuleFile(); }
+
   // Make a placeholder symbol for a Name that otherwise wouldn't have one.
   // It is not in any scope and always has MiscDetails.
   void MakePlaceholder(const parser::Name &, MiscDetails::Kind);

   set_allowForwardReferenceToDerivedType(false);
   if (derivedTypeInfo_.sequence) { // C740
     if (const auto *declType{GetDeclTypeSpec()}) {
-      if (!declType->AsIntrinsic() && !declType->IsSequenceType()) {
+      if (!declType->AsIntrinsic() && !declType->IsSequenceType() &&
+          !InModuleFile()) {
         if (GetAttrs().test(Attr::POINTER) &&
             context().IsEnabled(common::LanguageFeature::PointerInSeqType)) {
           if (context().ShouldWarn(common::LanguageFeature::PointerInSeqType)) {

       ApplyImplicitRules(*symbol);
     }
     if (checkIndexUseInOwnBounds_ &&
-        *checkIndexUseInOwnBounds_ == name.source) {
+        *checkIndexUseInOwnBounds_ == name.source && !InModuleFile()) {
       Say(name,
           "Implied DO index '%s' uses an object of the same name in its bounds expressions"_port_en_US,
           name.source);