I think I "broke" mkoctfile for 3.4.1

[Jordi Gutiérrez Hermoso]

There's a change  I pushed on the stable branch for 3.4.1

    http://hg.savannah.gnu.org/hgweb/octave/rev/2c54fde0f397

which breaks building some Octave-Forge packages. It concerns with how
they are passing -Wall to mkoctfile. With my change, in imitation of
how you pass flags to ld through gcc, you should now pass it as
-W,-Wall. I couldn't figure out from mkoctfile's docstring if the
previous way of just using -Wall worked coincidentally, but I think it
did. I changed this method of passing flags to gcc through mkoctfile
because I couldn't pass -std=c++0x, and it was inconvenient to do with
an environment variable for what I was trying to do for contract work
(which, btw, has just turned into a formal offer of employment to
improve Octave for this company, yay!).

Should this change be backed out? I think breaking mkoctfile this way
and the missing symlink reported in the help mailing list is
sufficiently bad and I wish we had caught this before releasing 3.4.1.

- Jordi G. H.