The language spec permits empty statements after a fallthrough
    statement, so implement that.  Also give a better error message when a
    fallthrough statement is in the wrong place.  The test case for this
    is in the master repository, test/fixedbugs/issue14540.go, just not
    yet in the gccgo repository.
    
    Fixes golang/go#14538
    
    Reviewed-on: https://go-review.googlesource.com/91855

From-SVN: r257378