The BuildTarget to build. (optional)
An AssetBundle is only compatible with the specific platform that it was built for, so you must produce different builds of a given bundle to use
the assets on different platforms.
If targetPlatform is not specified, e.g. it is 0, then the targetPlatform and subtarget fields will all be determined from the current build settings.
See Also: EditorUserBuildSettings.activeBuildTarget.