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