unistring / gnulib build problem

[Andy Wingo]

Hi,

I recently updated gnulib to the latest version on both stable-2.0 and
master, which is nice because we haven't done that for a while.  There
was a bug in the new mktime module that they added, and which Ludovic
and Paul Eggert tracked down and fixed.  Since then on my machine, all
systems are go and ready for release.

However.  Hydra is showing errors:

  https://hydra.nixos.org/build/37443729/log/raw

I believe the source of the problem is that Hydra's unistring is 0.9.3,
whereas Ludovic and I have been building with 0.9.6.  Gnulib has most
(or possibly all, I'm not sure) of unistring available as gnulib
modules, which is kinda cool if you want to not *require* a system
unistring.  However it gets tricky, because sometimes other gnulib
modules depend on the unistring modules in gnulib itself
(e.g. striconveh); in that case the gnulib modules have a higher
unistring requirement (0.9.4) than we do, which produces this error.
Specifically unistr.h is getting generated on Hydra and not on my
machine, leading to the problem.

We have a few options:

 1. Revert the gnulib update.

 2. Bump the libunistring required version.

 3. Hack gnulib.

(1) is possible but not great.  I fear that (2) is difficult because
0.9.3 is the de-facto widely-deployed unistring:

  http://packages.ubuntu.com/search?keywords=libunistring

I will look into (3) but suggestions are appreciated.

Andy