message: [DebugLine] Be more robust in geussing the path style
  My previous change didn't fix the Windows bot. This patch is an attempt
  to make guessing the path style more robust by first looking at the
  compile dir and falling back to the actual file if that's unsuccessful.
diff: @@ -186,6 +186,8 @@ ParseSupportFilesFromPrologue(const lldb::ModuleSP &module,
  FileSpecList support_files;
  support_files.Append(first_file);
  + llvm::Optional<FileSpec::Style> compile_dir_style =
  + FileSpec::GuessPathStyle(compile_dir);
  const size_t number_of_files = prologue.FileNames.size();
  for (size_t idx = 1; idx <= number_of_files; ++idx) {
  std::string original_file;
  @@ -198,9 +200,13 @@ ParseSupportFilesFromPrologue(const lldb::ModuleSP &module,
  continue;
  }
  - auto maybe_path_style = FileSpec::GuessPathStyle(original_file);
  - FileSpec::Style style =
  - maybe_path_style ? *maybe_path_style : FileSpec::Style::native;
  + FileSpec::Style style = FileSpec::Style::native;
  + if (compile_dir_style) {
  + style = *compile_dir_style;
  + } else if (llvm::Optional<FileSpec::Style> file_style =
  + FileSpec::GuessPathStyle(original_file)) {
  + style = *file_style;
  + }
  std::string remapped_file;
  if (!prologue.getFileNameByIndex(
  