linux-user: correctly align target_epoll_event

According to comments in /usr/include/linux/eventpoll.h,
poll_event is packed only on x86_64.

And to be sure fields are correctly aligned in epoll_data,
use abi_XXX types for all of them.

Moreover, fd type is wrong: fd is int, not ulong.

This has been tested with a ppc guest on an x86_64 host:
without this patch, systemd crashes (core).

CC: Alexander Graf <agraf@suse.de>
CC: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

linux-user/syscall_defs.h

@@ -2514,20 +2514,23 @@ struct target_mq_attr {
 #define FUTEX_CMD_MASK          ~(FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME)
 
 #ifdef CONFIG_EPOLL
+#if defined(TARGET_X86_64)
+#define TARGET_EPOLL_PACKED QEMU_PACKED
+#else
+#define TARGET_EPOLL_PACKED
+#endif
+
 typedef union target_epoll_data {
     abi_ulong ptr;
-    abi_ulong fd;
-    uint32_t u32;
-    uint64_t u64;
+    abi_int fd;
+    abi_uint u32;
+    abi_ullong u64;
 } target_epoll_data_t;
 
 struct target_epoll_event {
-    uint32_t events;
-#if defined(TARGET_ARM) || defined(TARGET_MIPS) || defined(TARGET_MIPS64)
-    uint32_t __pad;
-#endif
+    abi_uint events;
     target_epoll_data_t data;
-} QEMU_PACKED;
+} TARGET_EPOLL_PACKED;
 #endif
 struct target_rlimit64 {
     uint64_t rlim_cur;