何とやら is used to tell something in a roundabout way. In that case, it's for rephrasing the last half of a well-know proverb 腹が減っては戦[いくさ]はできぬ "An army marches on its stomach". This is a very common usage of 何とやら, e.g., うわさをすれば何とやら(=影) or 女心と何とやら(=秋の空).