Pure virtual functions

[Mark Mitchell <mark@xxxxxxxxxxxxxxxx>]

I remember raising this issue before, but it did not make it to the
issues list, or I am an idiot.  Either is possible.

We need to have a standard entry point to put in vtables to indicate a
pure virtual function.  (Some compilers use __pure_virtual, for
example.)  I think we want:

  extern "C" void __cxa_pure_virtual ();

Assuming there's no objection, let's just add this to the document for
review at the next meeting.

--
Mark Mitchell                   mark@xxxxxxxxxxxxxxxx
CodeSourcery, LLC               http://www.codesourcery.com