[flang] Use octal escapes for character literals in modfiles

[tskeith]

Summary

Character literals can be formatted using octal or hex escapes for
non-ascii characters. This is so that the program can be unparsed for
either pgf90 or gfortran to compile. But modfiles should not be affected
by that -- they should be consistent.

This changes causes modfiles to always have character literals formatted
with octal escapes.

[klausler]

flang/lib/Semantics/mod-file.cpp

109

Could use common::Restorer here instead of a flag and a destructor.

flang/lib/Semantics/mod-file.h

35

nit: should be explicit.

[tskeith]

Use common::ScopedSet instead of explicit destructor.

[tskeith]

flang/lib/Semantics/mod-file.cpp

109

Good idea, I've done that.

[klausler]

LGTM, thanks.

flang/lib/Semantics/mod-file.h

 
 using SourceName = parser::CharBlock;
 class Symbol;
 class Scope;
 class SemanticsContext;
 
 class ModFileWriter {
 public:
-  ModFileWriter(SemanticsContext &context) : context_{context} {}
+  explicit ModFileWriter(SemanticsContext &context) : context_{context} {}
   bool WriteAll();
 
 private:
   SemanticsContext &context_;
   // Buffer to use with raw_string_ostream
   std::string usesBuf_;
   std::string useExtraAttrsBuf_;
   std::string declsBuf_;

flang/lib/Semantics/mod-file.cpp

 //===-- lib/Semantics/mod-file.cpp ----------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "mod-file.h"
 #include "resolve-names.h"
+#include "flang/Common/restorer.h"
 #include "flang/Evaluate/tools.h"
 #include "flang/Parser/message.h"
 #include "flang/Parser/parsing.h"
 #include "flang/Semantics/scope.h"
 #include "flang/Semantics/semantics.h"
 #include "flang/Semantics/symbol.h"
 #include "flang/Semantics/tools.h"
 #include "llvm/Support/FileSystem.h"
private:
   template <typename T> void DoExpr(evaluate::Expr<T> expr) {
     for (const Symbol &symbol : evaluate::CollectSymbols(expr)) {
       DoSymbol(symbol);
     }
   }
 };
 
 bool ModFileWriter::WriteAll() {
+  // this flag affects character literals: force it to be consistent
+  auto restorer{
+      common::ScopedSet(parser::useHexadecimalEscapeSequences, false)};
   WriteAll(context_.globalScope());
   return !context_.AnyFatalError();
 }
 
 void ModFileWriter::WriteAll(const Scope &scope) {
   for (const auto &child : scope.children()) {
     WriteOne(child);
   }
 }
 
 void ModFileWriter::WriteOne(const Scope &scope) {
   if (scope.kind() == Scope::Kind::Module) {