[flang] Add conversions from EnumSet<Attr> to Attrs

This allows operations from EnumSet (e.g. `operator&`) to work as expected.

Original-commit: flang-compiler/f18@c8b8b74
Reviewed-on: flang-compiler/f18#675

flang/lib/semantics/attr.h

@@ -1,4 +1,4 @@
-// Copyright (c) 2018, NVIDIA CORPORATION.  All rights reserved.
+// Copyright (c) 2018-2019, NVIDIA CORPORATION.  All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -36,6 +36,8 @@ class Attrs : public common::EnumSet<Attr, Attr_enumSize> {
 
 public:
   using enumSetType::enumSetType;
+  Attrs(const enumSetType &attrs) : enumSetType(attrs) {}
+  Attrs(enumSetType &&attrs) : enumSetType(std::move(attrs)) {}
   constexpr bool HasAny(const Attrs &x) const { return !(*this & x).none(); }
   constexpr bool HasAll(const Attrs &x) const { return (~*this & x).none(); }
   // Internal error if any of these attributes are not in allowed.

flang/lib/semantics/mod-file.cc

@@ -288,8 +288,7 @@ void ModFileWriter::PutSubprogram(const Symbol &symbol) {
     bindAttrs.set(Attr::BIND_C, true);
     attrs.set(Attr::BIND_C, false);
   }
-  Attrs prefixAttrs{subprogramPrefixAttrs};
-  prefixAttrs &= attrs;
+  Attrs prefixAttrs{subprogramPrefixAttrs & attrs};
   // emit any non-prefix attributes in an attribute statement
   attrs &= ~subprogramPrefixAttrs;
   std::stringstream ss;

flang/lib/semantics/resolve-names.cc

@@ -1999,8 +1999,7 @@ static void ConvertToUseError(
 
 void ModuleVisitor::AddUse(
     const SourceName &location, Symbol &localSymbol, const Symbol &useSymbol) {
-  localSymbol.attrs() = useSymbol.attrs();
-  localSymbol.attrs() &= ~Attrs{Attr::PUBLIC, Attr::PRIVATE};
+  localSymbol.attrs() = useSymbol.attrs() & ~Attrs{Attr::PUBLIC, Attr::PRIVATE};
   localSymbol.flags() = useSymbol.flags();
   if (auto *useDetails{localSymbol.detailsIf<UseDetails>()}) {
     const Symbol &ultimate{localSymbol.GetUltimate()};