`configure' slightly broken in texinfo tree

[Nix]

Jeffrey A Law writes:
>   > The symptom is simple: upon typing `configure' (yes, even straight
>   > `configure' without any options at all), you get this:
> I just installed bash-2.02 and configured (on my i586-pc-linux-gnu laptop) and
> it configured just fine.

Whatever it is, it isn't bash - or not bash alone. I just built a
`bog-standard' bash without any options, with the standard CFLAGS &c,
with gcc-2.7.2.3, and configuring using that as my default shell gave
the same symptoms.

Hence I think we can rule bash bugs out, unless I somehow received a
corrupted bash source tarball long ago (not particularly likely).

> Something more subtle is going on.  I'd like to know what it is before we
> start hacking up texinfo (which we generally want to avoid doing, the closer
> it is to the standard distributions, the better).

What mystifies me is what the code in said configure.in is meant to
do. It reads

# We do this for the sake of a more helpful warning in doc/Makefile.
TEXMF='$(datadir)/texmf'

Am I being thoroughly thick, or will this execute the command named
`datadir', substitute its output into the command line, and stick a
`/texmf' on the end?

Given that

i) there is a variable named `datadir', and
ii) there is not guaranteed to be a command named `datadir', and,
    indeed, on my system there is not, and
iii) the *intent* of the code is probably to stick the expansion of the
     variable named `datadir' on the front of `/texmf', to get the
     probable location of the TeX data directory

how does it ever work on anyone's system? Do most people have a
command `datadir' that outputs the value of ${datadir} on stdout? Do
most people have some curious shell feature that turns unknown command
`foo' into a shell function that returns the variable named `foo'?

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