LONDON — Beset by warnings of “corrosive complacency” from defense heavyweights, Keir Starmer is eyeing a stitched-together funding fix for the British armed forces that avoids a direct confrontation with his own MPs over the soaring cost of social security. The U.K. prime minister is expected to resist calls for a major change to the country's welfare system to pay for a massive promised uplift in defense spending. That leaves him searching for more limited savings from across government