Depends which way the cars are turning if one is going left and the other right i'd say the one going left has right of way as he is not crossing anyones line, if both going right they should meet in the middle and go round each other.
In theory they should pass each other offside to offside at all times but in practice you should always expect the unexpected. You definitely shouldn't cut across the other car's line.
Probably the car that arrived at the junction first has the right of way. Thats how it works in Canada where there are lots of this type of junction in the suburbs