latest snapshot won't find C++ header files

[Jeffrey A Law]

  In message < orww6dzk4d.fsf@araguaia.dcc.unicamp.br >you write:
  > Alexandre Oliva <oliva@dcc.unicamp.br> writes:
  > 
  > > The following change has caused cppp to stop finding C++ header files,
  > > for two reasons.  First, it looks for include/g++, instead of
  > > include/g++-2, where libstdc++ installs them now.  Second, because
  > > include/g++-2 is architecture independent, so it is installed into
  > > $prefix, but ${libdir}/${unlibsubdir} is within $exec_prefix.
  > 
  > A closer look revealed that the current code attempts to do the right
  > thing, even when $prefix is different from $exec_prefix, but it seems
  > to assume $exec_prefix must be a subdirectory of $prefix, which is not
  > always true.  Why can't we just stay with $(gxx_include_dir) and
  > $(includedir) as cpplib.o still does?
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.  There's another patch in the pipeline to deal with finding
cc1, cpp, after relocating a tree.

jeff