Flightgear "asserts" with todays mesa git on RS880.

...
Enabling ATI viewport hack
util/u_blitter.c:1728:util_blitter_clear_buffer: Assertion `!"Streamout unsupported in util_blitter_clear_buffer()"' failed.

Program received signal SIGTRAP, Trace/breakpoint trap.
0x00007fffea44c9e8 in _debug_assert_fail (expr=0x7fffea6c1030 "!\"Streamout unsupported in util_blitter_clear_buffer()\"", 
    file=0x7fffea6c0cf7 "util/u_blitter.c", line=1728, function=0x7fffea6c10e0 <__func__.8464> "util_blitter_clear_buffer")
    at util/u_debug.c:278
278           os_abort();
(gdb) bt
#0  0x00007fffea44c9e8 in _debug_assert_fail (expr=0x7fffea6c1030 "!\"Streamout unsupported in util_blitter_clear_buffer()\"", 
    file=0x7fffea6c0cf7 "util/u_blitter.c", line=1728, function=0x7fffea6c10e0 <__func__.8464> "util_blitter_clear_buffer")
    at util/u_debug.c:278
#1  0x00007fffea45a558 in util_blitter_clear_buffer (blitter=0x132fec0, dst=0x1494dc0, offset=0, size=34816, num_channels=1, 
    clear_value=0x7fffffffbc00) at util/u_blitter.c:1728
#2  0x00007fffea554470 in r600_clear_buffer (ctx=0x1326520, dst=0x1494dc0, offset=0, size=34816, value=0) at r600_blit.c:645
#3  0x00007fffea5f5c54 in r600_screen_clear_buffer (rscreen=0x1325e70, dst=0x1494dc0, offset=0, size=34816, value=0)
    at r600_pipe_common.c:272
#4  0x00007fffea5f91fb in r600_texture_allocate_htile (rscreen=0x1325e70, rtex=0x1525e50) at r600_texture.c:488
#5  0x00007fffea5f9487 in r600_texture_create_object (screen=0x1325e70, base=0x7fffffffcba0, pitch_in_bytes_override=0, buf=0x0, 
    surface=0x7fffffffbda0) at r600_texture.c:549
#6  0x00007fffea5f9d5b in r600_texture_create (screen=0x1325e70, templ=0x7fffffffcba0) at r600_texture.c:702
#7  0x00007fffea55d6a1 in r600_resource_create (screen=0x1325e70, templ=0x7fffffffcba0) at r600_resource.c:38
#8  0x00007fffea604f50 in dri2_drawable_process_buffers (ctx=0x13000b0, drawable=0x1523a60, buffers=0x14964b0, buffer_count=1, 
    atts=0x1524fb0, att_count=2) at dri2.c:352
#9  0x00007fffea6052fa in dri2_allocate_textures (ctx=0x13000b0, drawable=0x1523a60, statts=0x1524fb0, statts_count=2) at dri2.c:471
#10 0x00007fffea60356b in dri_st_framebuffer_validate (stctx=0x13d59a0, stfbi=0x1523a60, statts=0x1524fb0, count=2, out=0x7fffffffcd50)
    at dri_drawable.c:83
#11 0x00007fffea2da890 in st_framebuffer_validate (stfb=0x1524b60, st=0x13d59a0) at ../../src/mesa/state_tracker/st_manager.c:192
#12 0x00007fffea2db973 in st_api_make_current (stapi=0x7fffeaa43de0 <st_gl_api>, stctxi=0x13d59a0, stdrawi=0x1523a60, streadi=0x1523a60)
    at ../../src/mesa/state_tracker/st_manager.c:722
#13 0x00007fffea60232e in dri_make_current (cPriv=0x136acf0, driDrawPriv=0x1495d80, driReadPriv=0x1495d80) at dri_context.c:240
#14 0x00007fffea1002e3 in driBindContext (pcp=0x136acf0, pdp=0x1495d80, prp=0x1495d80) at dri_util.c:380
#15 0x00007ffff5a3f3db in dri2_bind_context (context=0x1306f50, old=0x7ffff5c5c4a0 <dummyContext>, draw=104857603, read=104857603)
    at dri2_glx.c:172
#16 0x00007ffff5a04d76 in MakeContextCurrent (dpy=0x12f0bd0, draw=104857603, read=104857603, gc_user=0x1306f50) at glxcurrent.c:269
#17 0x00007ffff5a04e97 in glXMakeCurrent (dpy=0x12f0bd0, draw=104857603, gc=0x1306f50) at glxcurrent.c:303
#18 0x00007ffff66b0d0a in osgViewer::GraphicsWindowX11::makeCurrentImplementation() () from /usr/lib64/libosgViewer.so.80
#19 0x00007ffff600471d in osg::GraphicsContext::makeCurrent() () from /usr/lib64/libosg.so.80
#20 0x00007ffff66a9988 in osgViewer::ViewerBase::renderingTraversals() () from /usr/lib64/libosgViewer.so.80
#21 0x0000000000b2d7a5 in fgOSMainLoop() ()
#22 0x000000000064317a in fgMainInit(int, char**) ()
#23 0x000000000060a474 in main ()