We need this because now that __createBinding is used by __exportStar to create live-updating getters, if you had input like

export * from "mod";
export const nameFromMod = 0;

we'd output

__exportStar(exports, require("mod"));
exports.nameFromMod = 0;

the assignment will throw because the __exportStar made a getter which can't be overridden with a simple assignment. By emitting

exports.nameFromMod = void 0;
__exportStar(exports, require("mod"));
exports.nameFromMod = 0;

we prevent __exportStar from overwriting nameFromMod with a getter (so the assignment succeeds).

This also neatly ensures all export names are available to reexport when resolving within a circular module graph.