Add ice40_opt test

tests/ice40/ice40_opt.ys

@@ -0,0 +1,24 @@
+read_verilog -icells -formal <<EOT
+module top(input CI, I0, output CO, O);
+    wire A = 1'b0, B = 1'b0;
+	\$__ICE40_CARRY_WRAPPER #(
+		//    A[0]: 1010 1010 1010 1010
+		//    A[1]: 1100 1100 1100 1100
+		//    A[2]: 1111 0000 1111 0000
+		//    A[3]: 1111 1111 0000 0000
+		.LUT(~16'b 0110_1001_1001_0110)
+	) fadd (
+		.A(A),
+		.B(B),
+		.CI(CI),
+		.I0(I0),
+		.I3(CI),
+		.CO(CO),
+		.O(O)
+	);
+endmodule
+EOT
+
+equiv_opt -assert -map +/ice40/cells_map.v -map +/ice40/cells_sim.v ice40_opt
+design -load postopt
+select -assert-count 1 t:$lut