i965: Emit conditional code updates as required for GLSL VS if statements.

Previously, we'd be branching based on whatever condition code happened to be
laying around.
(cherry picked from commit 7007f8b352)

src/mesa/drivers/dri/i965/brw_vs_emit.c

@@ -1448,6 +1448,19 @@ void brw_vs_emit(struct brw_vs_compile *c )
 				    "unknown");
       }
 
+      /* Set the predication update on the last instruction of the native
+       * instruction sequence.
+       *
+       * This would be problematic if it was set on a math instruction,
+       * but that shouldn't be the case with the current GLSL compiler.
+       */
+      if (inst->CondUpdate) {
+	 struct brw_instruction *hw_insn = &p->store[p->nr_insn - 1];
+
+	 assert(hw_insn->header.destreg__conditionalmod == 0);
+	 hw_insn->header.destreg__conditionalmod = BRW_CONDITIONAL_NZ;
+      }
+
       if ((inst->DstReg.File == PROGRAM_OUTPUT)
           && (inst->DstReg.Index != VERT_RESULT_HPOS)
           && c->output_regs[inst->DstReg.Index].used_in_src) {