package/poppler: fix build with gcc 11

package/poppler: fix build with gcc 11

Fix the following build failure with gcc 11:

In file included from /tmp/instance-0/output-1/host/arm-buildroot-linux-gnueabihf/sysroot/usr/include/glib-2.0/glib/gthread.h:32,
                 from /tmp/instance-0/output-1/host/arm-buildroot-linux-gnueabihf/sysroot/usr/include/glib-2.0/glib/gasyncqueue.h:32,
                 from /tmp/instance-0/output-1/host/arm-buildroot-linux-gnueabihf/sysroot/usr/include/glib-2.0/glib.h:32,
                 from /tmp/instance-0/output-1/host/arm-buildroot-linux-gnueabihf/sysroot/usr/include/glib-2.0/gobject/gbinding.h:28,
                 from /tmp/instance-0/output-1/host/arm-buildroot-linux-gnueabihf/sysroot/usr/include/glib-2.0/glib-object.h:22,
                 from /tmp/instance-0/output-1/build/poppler-0.84.0/glib/poppler.h:22,
                 from /tmp/instance-0/output-1/build/poppler-0.84.0/glib/poppler-action.cc:19:
/tmp/instance-0/output-1/build/poppler-0.84.0/glib/poppler-action.cc: In function 'GType poppler_dest_get_type()':
/tmp/instance-0/output-1/build/poppler-0.84.0/glib/poppler-private.h:155:13: error: argument 2 of '__atomic_load' must not be a pointer to a 'volatile' type
  155 |         if (g_once_init_enter (&g_define_type_id__volatile)) {                        \
      |             ^~~~~~~~~~~~~~~~~
/tmp/instance-0/output-1/build/poppler-0.84.0/glib/poppler-action.cc:28:1: note: in expansion of macro 'POPPLER_DEFINE_BOXED_TYPE'
   28 | POPPLER_DEFINE_BOXED_TYPE (PopplerDest, poppler_dest, poppler_dest_copy, poppler_dest_free)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/dfcaac6487aaeb10412c3fe72a23135f8a70fefe

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>