limit glibc symbol by version script

[Nix]

On Wed, 12 Jul 2006, Steven Munroe gibbered uncontrollably:
> Nix wrote:
>>This isn't often tested, as far as I can tell: my attempt to build
>>with an oldest-abi of 2.4 failed on i386 (I didn't investigate
>>further: foolish of me).
>>
>>  
> Then try:
> 
>   --disable-versioning    do not include versioning information in the
> library objects

Yeah, that would probably have worked, except that I didn't want to
disable versioning, but rather to keep it from this point forward.

Still, it's hardly killingly nasty: by my rough estimate there's
less than 100K of code in glibc that's specific to older versions
anyhow.