[PATCHv2] malloc: Make sure tcache_key is odd enough

[Florian Weimer]

* Samuel Thibault:

> I'm sure re-reading everything and I don't see where logic fails: that
> line *is* 80 characters-long, so it doesn't wraps around in usual
> 80-char terminals.

I thought that exactly 80 columns was acceptable, but the GNU
standards disagree:

| Please keep the length of source lines to 79 characters or less, for
| maximum readability in the widest range of environments.

<https://www.gnu.org/prep/standards/html_node/Formatting.html>