latest snapshot won't find C++ header files

[Jeffrey A Law]

  In message < orzpb8rrxw.fsf@araguaia.dcc.unicamp.br >you write:
  > --Multipart_Wed_Oct__7_18:19:08_1998-1
  > Content-Type: text/plain; charset=US-ASCII
  > 
  > Jeffrey A Law <law@cygnus.com> writes:
  > 
  > >   In message < orww6dzk4d.fsf@araguaia.dcc.unicamp.br >you write:
  > >> Alexandre Oliva <oliva@dcc.unicamp.br> writes:
  > 
  > >> it seems to assume $exec_prefix must be a subdirectory of $prefix,
  > >> which is not always true
  > 
  > > The point behind libunsubdir is to make it easier to move the installed
  > > tree around without having to fart around with GCC_EXEC_PREFIX or rebuild
  > > the tools.
  > 
  > I see, but the assumption that exec_prefix must be prefix or a
  > subdirectory thereof may break existing behavior; isn't it too strong?
  > 
  > Anyway, here's a patch that should simplify things...  Ok to install?
Let's slow down a little.  I don't see that anything got simpler, particularly
when we also deal with Manfred's problem.

We have two problems with the unlibsubdir code, and I think they both can be
fixed by having configure substitute in a suitable value for unlibsubdir
instead of blindly using ../../..

See my message to Manfred from last night.

jeff