Enable -Wself-assign-memvar for Mesa, merge upstream fix for the one violation

third_party/mesa/MesaLib/src/glsl/ir.h

Index: third_party/mesa/MesaLib/src/glsl/ir.h
diff --git a/third_party/mesa/MesaLib/src/glsl/ir.h b/third_party/mesa/MesaLib/src/glsl/ir.h
index fa246b5e57073308fa7fd15c19ac5c6f5e75bc09..5aa7c6da892bb0459b91307a8836567de661c0df 100644
--- a/third_party/mesa/MesaLib/src/glsl/ir.h
+++ b/third_party/mesa/MesaLib/src/glsl/ir.h
@@ -989,7 +989,6 @@ public:
    {
       this->ir_type = ir_type_loop_jump;
       this->mode = mode;
-      this->loop = loop;
    }
 
    virtual ir_loop_jump *clone(void *mem_ctx, struct hash_table *) const;
@@ -1013,9 +1012,6 @@ public:
 
    /** Mode selector for the jump instruction. */
    enum jump_mode mode;
-private:
-   /** Loop containing this break instruction. */
-   ir_loop *loop;
 };
 
 /**