syscall: fix epoll_event padding on linux/arm64

EpollEvent needs padding before Fd as was already done for x/sys/unix in
CL 21971.

Fixes #35479

Change-Id: Iee963f9e26d0a23d16d6bab736fd71ae7f502894
Reviewed-on: https://go-review.googlesource.com/c/go/+/206838
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/syscall/types_linux.go

@@ -111,7 +111,7 @@ typedef struct {} ptracePer;
 // The real epoll_event is a union, and godefs doesn't handle it well.
 struct my_epoll_event {
 	uint32_t events;
-#if defined(__ARM_EABI__) || (defined(__mips__) && _MIPS_SIM == _ABIO32)
+#if defined(__ARM_EABI__) || defined(__aarch64__) || (defined(__mips__) && _MIPS_SIM == _ABIO32)
 	// padding is not specified in linux/eventpoll.h but added to conform to the
 	// alignment requirements of EABI
 	int32_t padFd;

src/syscall/ztypes_linux_arm64.go

@@ -564,6 +564,7 @@ type Ustat_t struct {
 
 type EpollEvent struct {
 	Events uint32
+	_      int32
 	Fd     int32
 	Pad    int32
 }