glsl: Add ir_binop_carry and ir_binop_borrow.

Calculates the carry out of the addition of two values and the
borrow from subtraction respectively. Will be used in uaddCarry() and
usubBorrow() built-in implementations.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/glsl/ir_builder.cpp

@@ -221,6 +221,16 @@ ir_expression *div(operand a, operand b)
    return expr(ir_binop_div, a, b);
 }
 
+ir_expression *carry(operand a, operand b)
+{
+   return expr(ir_binop_carry, a, b);
+}
+
+ir_expression *borrow(operand a, operand b)
+{
+   return expr(ir_binop_borrow, a, b);
+}
+
 ir_expression *round_even(operand a)
 {
    return expr(ir_unop_round_even, a);