I had the same problem. I moved it from the build.cs to target.cs.
public class test416Target : TargetRules
{
public test416Target(TargetInfo Target) : base(Target)
{
Type = TargetType.Game;
UEBuildConfiguration.bForceEnableExceptions = true;
ExtraModuleNames.AddRange( new string] { "test416" } );
}
}