Fix for c++/13387 -> libstdc++ regressions

[Paolo Carlini]

Hi,

I'm trying to understand which patch, went in on December the 16th
is causing libstdc++ regressions on many (64-bit) platforms:

    http://gcc.gnu.org/ml/gcc/2003-12/msg01078.html

After having tried reverting a few, I have discovered that Richard
Sandiford (most probably) already found it!

    http://gcc.gnu.org/ml/gcc-patches/2003-12/msg01703.html

Nathan, Mark, others, could you please provide some feedback and
answer Richard's concerns?

Thanks,
Paolo.