devel/libindicator: fix build on powerpc64 elfv1 and remove stale CFLAGS

Build on both elfv1 and elfv2 passes fine. Other architectures are untested, but they currently don't have Rust available, making build impossible.

Require newer GCC to build on elfv1:
cc1: warnings being treated as errors
In file included from /usr/local/include/glib-2.0/glib/gthread.h:34,

from /usr/local/include/glib-2.0/glib/gasyncqueue.h:32,
from /usr/local/include/glib-2.0/glib.h:32,
from /usr/local/include/gtk-3.0/gdk/gdkconfig.h:13,
from /usr/local/include/gtk-3.0/gdk/gdk.h:30,
from /usr/local/include/gtk-3.0/gtk/gtk.h:30,
from indicator-loader.c:25:

/usr/local/include/glib-2.0/glib/gutils.h:336: warning: 'GVoidFunc' is deprecated