What was the margin of victory when the winning score was −12 (66-67-64-71=268)?
CREATE TABLE "pga_tour_wins_5" (
  "date" text,
  "tournament" text,
  "winning_score" text,
  "margin_of_victory" text,
  "runner_s_up" text
);
SELECT "margin_of_victory" FROM "pga_tour_wins_5" WHERE "winning_score"='−12 (66-67-64-71=268)';