[libstdc++] little cosmetics in configury

[Paolo Carlini]

Phil Edwards wrote:

>While looking over the ARM changes, I noticed that many of the comments
>were getting out of date and incorrect, so this fixes them up.
>
>A while back I said I'd fix up some of the unneeded defensive shell
>programming next time I was editing those files, so I did.
>
>Tested and committed.
>  
>
Phil, in the final commit I see an aclocal.m4 regenerated with aclocal 
version
1.7.9 instead of 1.8.5. Could you please check?

Thanks,
Paolo.