syscall: fix epoll_event struct for ppc64le/ppc64

The existing epoll_event structure used by many of
the epoll_* syscalls was defined incorrectly
for use with ppc64le & ppc64 in the syscall
directory.  This resulted in the caller getting
incorrect information on return from these
syscalls.  This caused failures in fsnotify as
well as builds with upstream Docker.  The
structure is defined correctly in gccgo.

This adds a pad field that is expected for
these syscalls on ppc64le, ppc64.
Fixes #15135

Fixes #15288

Change-Id: If7e8ea9eb1d1ca5182c8dc0f935b334127341ffd
Reviewed-on: https://go-review.googlesource.com/21582
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-on: https://go-review.googlesource.com/22207
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/syscall/types_linux.go

@@ -104,6 +104,9 @@ struct my_epoll_event {
 	// padding is not specified in linux/eventpoll.h but added to conform to the
 	// alignment requirements of EABI
 	int32_t padFd;
+#endif
+#ifdef  __powerpc64__
+	int32_t _padFd;
 #endif
 	int32_t fd;
 	int32_t pad;

src/syscall/ztypes_linux_ppc64.go

@@ -574,9 +574,10 @@ type Ustat_t struct {
 }
 
 type EpollEvent struct {
-	Events uint32
-	Fd     int32
-	Pad    int32
+	Events  uint32
+	X_padFd int32
+	Fd      int32
+	Pad     int32
 }
 
 const (

src/syscall/ztypes_linux_ppc64le.go

@@ -574,9 +574,10 @@ type Ustat_t struct {
 }
 
 type EpollEvent struct {
-	Events uint32
-	Fd     int32
-	Pad    int32
+	Events  uint32
+	X_padFd int32
+	Fd      int32
+	Pad     int32
 }
 
 const (