message: Simplify DWARFUnit::m_die_array swap() to use shrink_to_fit()
  rL145086 introduced m_die_array.shrink_to_fit() implemented by
  exact_size_die_array.swap, it was before LLVM became written in C++11.
diff: @@ -180,15 +180,7 @@ bool DWARFUnit::ExtractDIEsIfNeeded() {
  m_first_die = m_die_array.front();
  }
  - // Since std::vector objects will double their size, we really need to make a
  - // new array with the perfect size so we don't end up wasting space. So here
  - // we copy and swap to make sure we don't have any extra memory taken up.
  -
  - if (m_die_array.size() < m_die_array.capacity()) {
  - DWARFDebugInfoEntry::collection exact_size_die_array(m_die_array.begin(),
  - m_die_array.end());
  - exact_size_die_array.swap(m_die_array);
  - }
  + m_die_array.shrink_to_fit();
  ExtractDIEsEndCheck(offset);
  