[libstdc++,doc] Link maintenance for doc/xml/manual/documentation_hacking.xml

[Jonathan Wakely]

On 06/02/17 11:28 +0100, Gerald Pfeifer wrote:
>Before GCC 7 branches, I am trying to get as many links in our
>(non-wwwdocs) documentation fixed as possible.  Turns out libstdc++
>has a fair number that need attention.
>
>In documentation_hacking.xml I could not find a replacement document
>for DocBook Publishing Tools.  The other two changes were more straight-
>forward.
>
>(In particular, also note that "here" or "online" as names for links
>should be avoided, and this patch also improves one such case.)

Thanks, I always change such link names when I come across them, but I
expect we still have a few.