[PATCH 4/5] Fix typos in libstdc++.

[Jonathan Wakely]

I agree with all Paolo's comments.

Also libstdc++-v3/doc/html/ext/lwg-active.html is imported from
elsewhre so it's pointless fixing it, the upstream version comes from
https://github.com/cplusplus/LWG

Most of the changes are replacing British English with American
English, so low priority. I'll apply the correct parts of the patch
and commit it.

Thanks.