The Pentagon concluded that Alibaba Group Holding Ltd., Baidu Inc. and BYD Co. should be added to a list of companies that aid the Chinese military, according to a letter to Congress sent roughly three weeks before Donald Trump and Xi Jinping agreed to a broad trade truce.Deputy Defense Secretary Stephen Feinberg informed lawmakers of the conclusion in the Oct. 7 letter, a copy of which was seen by Bloomberg News, to the heads of the House and Senate Armed Services Committees....