unix: fix Pause on linux-arm64

Pause is a legacy syscall not available on linux-arm64. Use ppoll with
all args as 0 to emulate - this is the way musl libc does Pause when the
pause syscall isn't available.

With the changes in syscall_linux* and regenerating zsyscall_linux*,
this calling Pause on linux-arm64 works and returns EINTR as expected.

Change-Id: I88236290313f18c742d826e759e86ff260a8b383
Reviewed-on: https://go-review.googlesource.com/22014
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/unix/syscall_linux_amd64.go b/unix/syscall_linux_amd64.go
index 524ab52..721f24b 100644
--- a/unix/syscall_linux_amd64.go
+++ b/unix/syscall_linux_amd64.go
@@ -26,6 +26,7 @@
 //sys	Lchown(path string, uid int, gid int) (err error)
 //sys	Listen(s int, n int) (err error)
 //sys	Lstat(path string, stat *Stat_t) (err error)
+//sys	Pause() (err error)
 //sys	Pread(fd int, p []byte, offset int64) (n int, err error) = SYS_PREAD64
 //sys	Pwrite(fd int, p []byte, offset int64) (n int, err error) = SYS_PWRITE64
 //sys	Seek(fd int, offset int64, whence int) (off int64, err error) = SYS_LSEEK