linux-user/arm/syscall_nr.h: Add syscall number for ppoll

The list of ARM syscall numbers was missing the entry for ppoll,
which meant we were accidentally not providing it. (This wasn't
causing any practical issues beyond warnings about unimplemented
syscalls, because glibc will fall back to another code path if the
syscall isn't present.)
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NRiku Voipio <riku.voipio@linaro.org>

linux-user/arm/syscall_nr.h

@@ -339,7 +339,7 @@
 #define TARGET_NR_fchmodat			(333)
 #define TARGET_NR_faccessat			(334)
 #define TARGET_NR_pselect6			(335)
-					/* 336 for ppoll */
+#define TARGET_NR_ppoll                         (336)
 #define TARGET_NR_unshare			(337)
 #define TARGET_NR_set_robust_list		(338)
 #define TARGET_NR_get_robust_list		(339)