Switch to Mesa 7.9.

media-libs/mesa/files/7.9-add-discard.patch

+From 1eb7a81f2e43842acd59929ce65db2142b69134d Mon Sep 17 00:00:00 2001
+From: Kenneth Graunke <kenneth@whitecape.org>
+Date: Thu, 25 Nov 2010 05:33:07 +0000
+Subject: glsl: Add a virtual as_discard() method.
+
+NOTE: This is candidate for the 7.9 branch.
+---
+diff --git a/src/glsl/ir.h b/src/glsl/ir.h
+index 850033b..62bb0fd 100644
+--- a/src/glsl/ir.h
++++ b/src/glsl/ir.h
+@@ -122,6 +122,7 @@ public:
+    virtual class ir_if *                as_if()               { return NULL; }
+    virtual class ir_swizzle *           as_swizzle()          { return NULL; }
+    virtual class ir_constant *          as_constant()         { return NULL; }
++   virtual class ir_discard *           as_discard()          { return NULL; }
+    /*@}*/
+ 
+ protected:
+@@ -1122,6 +1123,11 @@ public:
+ 
+    virtual ir_visitor_status accept(ir_hierarchical_visitor *);
+ 
++   virtual ir_discard *as_discard()
++   {
++      return this;
++   }
++
+    ir_rvalue *condition;
+ };
+ /*@}*/
+--
+cgit v0.8.3-6-g21f6