syscall: on ARM GNU/Linux let Pipe fall back to pipe

Android O seems to require Pipe to call the pipe2 system call.
But kernel version 2.6.23 only supports pipe, not pipe2.
So try pipe2 first, then fall back to pipe.

Fixes #30549

Change-Id: I3c5d86e8e945a5ec8a0ecea7853302952c0476c4
Reviewed-on: https://go-review.googlesource.com/c/go/+/165217
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/syscall/syscall_linux_arm.go

@@ -19,12 +19,18 @@ func setTimeval(sec, usec int64) Timeval {
 	return Timeval{Sec: int32(sec), Usec: int32(usec)}
 }
 
+//sysnb pipe(p *[2]_C_int) (err error)
+
 func Pipe(p []int) (err error) {
 	if len(p) != 2 {
 		return EINVAL
 	}
 	var pp [2]_C_int
+	// Try pipe2 first for Android O, then try pipe for kernel 2.6.23.
 	err = pipe2(&pp, 0)
+	if err == ENOSYS {
+		err = pipe(&pp)
+	}
 	p[0] = int(pp[0])
 	p[1] = int(pp[1])
 	return

src/syscall/zsyscall_linux_arm.go

@@ -1138,6 +1138,16 @@ func Munlockall() (err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func pipe(p *[2]_C_int) (err error) {
+	_, _, e1 := RawSyscall(SYS_PIPE, uintptr(unsafe.Pointer(p)), 0, 0)
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func pipe2(p *[2]_C_int, flags int) (err error) {
 	_, _, e1 := RawSyscall(SYS_PIPE2, uintptr(unsafe.Pointer(p)), uintptr(flags), 0)
 	if e1 != 0 {