The Monday after last Thanksgiving, Mary Barra, chief executive officer of General Motors Co., announced the automaker’s biggest layoff since its 2009 bankruptcy. Five North American factories were marked for closure. Six thousand hourly jobs in the U.S. and Canada would soon be eliminated, and about 18,000 salaried employees would have until the end of the year to consider a buyout package. GM needed more than a third of the salaried personnel to accept. Fewer than 2,000 did. The remainder would have to be let go, which they were, starting in February.