-e: over the course of several releases more and more items ended up being added to the root folder of a standalone build. so you can no longer build different version into the same folder. See also https://forum.unity.com/threads/unity-2017-2-unityplayer-dll-being-created-after-build-22mb.500158/

--things being added to the standalone build root:
---2017.2: UnityPlayer.dll
---2018.1: UnityCrashandler.exe
---2018.1: Mono folder

-repro:
--create new project on 2018.1
--make a standalone build
--NOTICE that apart form the *.exe and the *_Data all the other things got added into the root folder