--without-lxml for Flatpak builds

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 1462b2784f "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/51321
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

configure.ac

@@ -2082,6 +2082,13 @@ AC_ARG_WITH(iwyu,
          Use only if you are hacking on it.]),
 ,)
 
+libo_FUZZ_ARG_WITH(lxml,
+    AS_HELP_STRING([--without-lxml],
+        [gla11y will use python lxml when available, potentially building a local copy if necessary.
+         --without-lxml tells it to not use python lxml at all, which means that gla11y will only
+         report widget classes and ids.]),
+,)
+
 dnl ===================================================================
 dnl Branding
 dnl ===================================================================
@@ -8157,6 +8164,7 @@ if test $enable_python = system; then
     PYTHON_FOR_BUILD=$PYTHON
 fi
 
+if test "$with_lxml" != no; then
     if test -z "$PYTHON_FOR_BUILD"; then
         case $build_os in
             cygwin)
@@ -8188,6 +8196,7 @@ else
             esac
         fi
     fi
+fi
 
 dnl By now enable_python should be "system", "internal" or "no"
 case $enable_python in

distro-configs/LibreOfficeFlatpak.conf

@@ -9,6 +9,7 @@
 --with-vendor=The Document Foundation
 --without-export-validation
 --without-junit
+--without-lxml
 --without-system-apache-commons
 --without-system-beanshell
 --without-system-bluez