message: Construct SourceManager with UserFilesAreVolatile
  Fix Close
  In clang, it may be worth generalizing UserFilesAreVolatile (introduced in rC160074) to FilesAreVolatile.
diff: @@ -1255,6 +1255,8 @@ Index(SemaManager *manager, WorkingFiles *wfiles, VFS *vfs,
  Clang->setVirtualFileSystem(FS);
  Clang->createFileManager();
  #endif
  + Clang->setSourceManager(new SourceManager(Clang->getDiagnostics(),
  + Clang->getFileManager(), true));
  IndexParam param(*vfs, no_linkage);
  auto DataConsumer = std::make_shared<IndexDataConsumer>(param);
  