This fixes double-definitions in bsd-user builds when using the UST
tracing backend (which indirectly includes the system's "syscall.h").
Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
