Use CXXPseudoDestructorExpr as the stored representation for dependent

expressions that look like pseudo-destructors, e.g.,

  p->T::~T()

where p has dependent type.

At template instantiate time, we determine whether we actually have a
pseudo-destructor or a member access, and funnel down to the
appropriate routine in Sema.

Fixes PR6380.

llvm-svn: 97092