[Frontend] Clean up some dead code in PrecompiledPreamble. NFC

    // A main method used to construct TempPCHFile.

    static llvm::ErrorOr<TempPCHFile> CreateNewPreamblePCHFile();

    /// Call llvm::sys::fs::createTemporaryFile to create a new temporary file.

    static llvm::ErrorOr<TempPCHFile> createInSystemTempDir(const Twine &Prefix,

                                                            StringRef Suffix);

    /// Create a new instance of TemporaryFile for file at \p Path. Use with

    /// extreme caution, there's an assertion checking that there's only a

    /// single instance of TempPCHFile alive for each path.

    static llvm::ErrorOr<TempPCHFile> createFromCustomPath(const Twine &Path);

  private:

    TempPCHFile(std::string FilePath);

  // FIXME: This is a hack so that we can override the preamble file during

  // crash-recovery testing, which is the only case where the preamble files

  // are not necessarily cleaned up.

  const char *TmpFile = ::getenv("CINDEXTEST_PREAMBLE_FILE");

  if (TmpFile)

    return TempPCHFile::createFromCustomPath(TmpFile);

  return TempPCHFile::createInSystemTempDir("preamble", "pch");

}

  if (const char *TmpFile = ::getenv("CINDEXTEST_PREAMBLE_FILE"))

    return TempPCHFile(TmpFile);

llvm::ErrorOr<PrecompiledPreamble::TempPCHFile>

PrecompiledPreamble::TempPCHFile::createInSystemTempDir(const Twine &Prefix,

                                                        StringRef Suffix) {

  llvm::SmallString<64> File;

  // Using a version of createTemporaryFile with a file descriptor guarantees

  // that we would never get a race condition in a multi-threaded setting

  // (i.e., multiple threads getting the same temporary path).

  int FD;

  auto EC = llvm::sys::fs::createTemporaryFile(Prefix, Suffix, FD, File);

  auto EC = llvm::sys::fs::createTemporaryFile("preamble", "pch", FD, File);

  if (EC)

    return EC;

  // We only needed to make sure the file exists, close the file right away.

  return TempPCHFile(std::move(File).str());

}

llvm::ErrorOr<PrecompiledPreamble::TempPCHFile>

PrecompiledPreamble::TempPCHFile::createFromCustomPath(const Twine &Path) {

  return TempPCHFile(Path.str());

}

PrecompiledPreamble::TempPCHFile::TempPCHFile(std::string FilePath)

    : FilePath(std::move(FilePath)) {

  TemporaryFiles::getInstance().addFile(*this->FilePath);