unix: always use inotify_init1 over inotify_init on AMD64

ARM64 does this exact same thing, and in fact this is required on
Android 9, where Bionic now only allows inotify_init on 32-bit
platforms. Folks are running into this when using Android on
Chromebooks, which are keeping AMD64 Android alive. So, we change the
AMD64 behavior to model that of ARM64. However, since Go must run on
kernels between 2.6.27 and 2.6.23, we must still fall back to the
original call.

Fixes: https://lore.kernel.org/wireguard/CALv=V9Gv6apdWJ9P-80zf9bgByd=c3QqPhRHuw6o0_OaH0=W6g@mail.gmail.com
Change-Id: I183e82679cb7d702d12a35457920ccd422176254
Reviewed-on: https://go-review.googlesource.com/c/153318
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/syscall_linux_amd64.go

@@ -20,7 +20,17 @@ package unix
 //sysnb	Getgid() (gid int)
 //sysnb	Getrlimit(resource int, rlim *Rlimit) (err error)
 //sysnb	Getuid() (uid int)
-//sysnb	InotifyInit() (fd int, err error)
+//sysnb	inotifyInit() (fd int, err error)
+
+func InotifyInit() (fd int, err error) {
+	// First try inotify_init1, because Android's seccomp policy blocks the latter.
+	fd, err = InotifyInit1(0)
+	if err == ENOSYS {
+		fd, err = inotifyInit()
+	}
+	return
+}
+
 //sys	Ioperm(from int, num int, on int) (err error)
 //sys	Iopl(level int) (err error)
 //sys	Lchown(path string, uid int, gid int) (err error)

unix/zsyscall_linux_amd64.go

@@ -1806,7 +1806,7 @@ func Getuid() (uid int) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func InotifyInit() (fd int, err error) {
+func inotifyInit() (fd int, err error) {
 	r0, _, e1 := RawSyscall(SYS_INOTIFY_INIT, 0, 0, 0)
 	fd = int(r0)
 	if e1 != 0 {