syscall: fix EpollEvent padding on mips64{,le}

Like on other 64-bit GOARCHes, EpollEvent needs padding before Fd for
mips64 and mips64le.

Change-Id: I87773a1b305552ab4ed039623b40d2fff1f20d9b
Reviewed-on: https://go-review.googlesource.com/c/go/+/207298
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/syscall/types_linux.go

@@ -116,7 +116,8 @@ struct my_epoll_event {
 	// alignment requirements of EABI
 	int32_t padFd;
 #endif
-#if defined(__powerpc64__) || defined(__s390x__) || (defined(__riscv_xlen) && __riscv_xlen == 64)
+#if defined(__powerpc64__) || defined(__s390x__) || (defined(__riscv_xlen) && __riscv_xlen == 64) \
+		|| (defined(__mips__) && _MIPS_SIM == _MIPS_SIM_ABI64)
 	int32_t _padFd;
 #endif
 	int32_t fd;

src/syscall/ztypes_linux_mips64.go

@@ -569,6 +569,7 @@ type Ustat_t struct {
 
 type EpollEvent struct {
 	Events uint32
+	_      int32
 	Fd     int32
 	Pad    int32
 }

src/syscall/ztypes_linux_mips64le.go

@@ -569,6 +569,7 @@ type Ustat_t struct {
 
 type EpollEvent struct {
 	Events uint32
+	_      int32
 	Fd     int32
 	Pad    int32
 }