[rui314]

This patch makes cpp_demangle demangle the following names in the same
way as GNU and LLVM do.

_ZTVN2ns1AE
  before: {vtable(ns::A)}
  after:  vtable for ns::A

_ZTTN2ns1DE
  before: {vtt(ns::D)}
  after:  VTT for ns::D

_ZThn16_N2ns1C1gEv
  before: {virtual override thunk({offset(-16)}, ns::C::g())}
  after:  non-virtual thunk to ns::C::g()

_ZTv0_n32_N2ns1D1fEv
  before: {virtual override thunk({virtual offset(0, -32)}, ns::D::f())}
  after:  virtual thunk to ns::D::f()

_ZTCN2ns1DE16_NS_1WE
  before: construction vtable for ns::D-in-ns::W
  after:  construction vtable for ns::W-in-ns::D

The "after" lines match what c++filt prints.