build-sys: bring back an intltool-update workaround

build-sys: bring back an intltool-update workaround

Currently, 'make distcheck' fails with an error such as this:

    srcdir=../../po /usr/bin/intltool-update -m
    The following files contain translations and are currently not in use.
    Please consider adding these to the POTFILES.in file, located in the po/ directory.

    build2/src/core/org.freedesktop.systemd1.policy.in
    build3/src/core/org.freedesktop.systemd1.policy.in

    [...]

This is caused by a new behavior of autmake 1.15 which changed the
location of the build tree during 'make distcheck', and the fact that
intltool doesn't yet ignore that paths.

We used to have a workaround in configure.ac that makes the failing call
a no-op, but it was accidentially removed in 23756070
("remove gudev and gtk-doc").

Bring back that snipet for now, until intltool and automake sorted out
their issues and like each other again.

Also see

  https://bugs.launchpad.net/intltool/+bug/1117944