Add `/warnVacuousProofs` option #1955

Job	Run time
Boogie CI (Release, batch_mode=True)	4m 21s
Boogie CI (Release, batch_mode=False)	4m 30s
Boogie CI (Debug, batch_mode=False)	4m 37s
Boogie CI (Debug, batch_mode=True)	4m 37s
	18m 5s

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