linux-user: Check sigsetsize argument to syscalls

Many syscalls which take a sigset_t argument also take an argument
giving the size of the sigset_t.  The kernel insists that this
matches its idea of the type size and fails EINVAL if it is not.
Implement this logic in QEMU.  (This mostly just means some LTP test
cases which check error cases now pass.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
