where the Yocto-based GNOME SDK provides no python lxml, but building LO's
internal one fails because it internally uses {xml2,xslt}-config, and those are
broken by (mis?-)design in Yocto, just returning with exit code 1.

It didn't work well to pass applications of pkg-config into the external/lxml
build as replacements for --with-{xml2,xslt}-config (as is successfully done
elsewhere with 1462b278 "Adapt the
external/redland/raptor/xml2-config.patch to raptor2-2.0.15"), so just run
gla11y in its slightly limited form without lxml in the Flatpak build.

Change-Id: I2d42901373c8c861b16da385c37bcc24d6e783fd
Reviewed-on: https://gerrit.libreoffice.org/51321Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>