package/pipewire: needs gcc >= 5

package/pipewire: needs gcc >= 5

spa (i.e. plugins which can be disabled but also tools which can't be
disabled) fails to build on gcc 4.8 since bump to version 0.3.26 in
commit a6d88d3ba5e30e11f4d726f341bc56c1be7c71c9:

In file included from ../spa/include/spa/pod/builder.h:34:0,
                 from ../spa/include/spa/param/audio/format-utils.h:34,
                 from ../spa/plugins/audioconvert/test-audioadapter.c:36:
../spa/include/spa/utils/hook.h:57:50: error: initializer element is not constant
 #define SPA_CALLBACKS_INIT(_funcs,_data) (struct spa_callbacks){ _funcs, _data, }
                                                  ^

Fixes:
 - http://autobuild.buildroot.org/results/e7a36ec7166a287667572e5140685e6371a9f107

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>