Fix XORG_WITH_XMLTO to work with xmlto >= 0.0.27

Starting with xmlto version 0.0.27 the return code of
  xmlto --skip-validation txt conftest.xml
is non-zero if conftest.xml is an empty file.

As a consequence the macro XORG_WITH_XMLTO returns
  "xmlto cannot generate text format, this format skipped"
and therefore libraries like libxi, libxdmcp and others won't convert
docbook XML to text format.

This changed behavior was introduced with the following change in xmlto:
  xmlto.in: use correctly exit code from xsltproc
See also: https://fedorahosted.org/xmlto/changeset/77

This patch fixes this by additionally testing xmlto with a non-empty XML
file.

More details can be found at:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=613674

Thanks to Peter Pearse, Helmut Grohne and Gaetan Nadon.

v2: To maintain compatibility with older xorg tarballs don't replace
    the original test with the empty XML file but instead add a fallback
    to additionally test with a non-empty XML file if the original test fails.
    Use the alternate solution with <x></x> to skip compatibility issues
    with different docbook versions.

Signed-off-by: Andreas Boll <andreas.boll.dev@gmail.com>
Reviewed-by: Gaetan Nadon <memsize@videotron.ca>
Signed-off-by: Julien Cristau <jcristau@debian.org>

0 files changed, 0 insertions, 0 deletions