mesa: List new source file in SConscript.
diff --git a/src/mesa/SConscript b/src/mesa/SConscript
index 5cf3bfd..da4026b 100644
--- a/src/mesa/SConscript
+++ b/src/mesa/SConscript
@@ -164,6 +164,7 @@
 		'state_tracker/st_cb_readpixels.c',
 		'state_tracker/st_cb_strings.c',
 		'state_tracker/st_cb_texture.c',
+		'state_tracker/st_cb_viewport.c',
 		'state_tracker/st_context.c',
 		'state_tracker/st_debug.c',
 		'state_tracker/st_draw.c',