[tlbuild] tl25/dev: building failure on OpenBSD

[Karl Berry]

Hi Robert and Bruno and all,

    makeinfo: unknown option -- set

Ah. The proximate cause of this happening is that I forgot to commit a
new tlbuild.info when I tweaked tlbuild.texi, to avoid the makeinfo
calls in the first place. Done now.

    bh> Build/source/README.1prerequisites does not state a minimum
    version of 'makeinfo'

The versions we use for building are currently listed in a later
node: https://tug.org/texinfohtml/tlbuild.html#Build-system-tools
I'll move that info to the prereq chapter, where it clearly belongs.

Despite listing the latest version there, I have tried to refrain from
using the latest features of Texinfo (or other tools), as far as the
document source goes. I'm not surprised 4.8 didn't work, though.
There's no good alternative to the --set option I'm passing to makeinfo,
as far as I know. (I have to adapt to the output from pod2texi.)

Thanks,
Karl

P.S. The latest versions of the autotools are truly required, though, at
least if it's necessary to exactly reproduce the build environment
(which it isn't always). Probably without any distro patches.