unix: add missing dup2 syscall on mips64*

After this commit the testsuite passes on mips64le.

Fixes golang/go#20340.

Change-Id: I6b3f673674af107fd6d249ccf5e695e0e50a41bb
Reviewed-on: https://go-review.googlesource.com/43430Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/syscall_linux_mips64x.go

@@ -7,6 +7,7 @@
 
 package unix
 
+//sys	Dup2(oldfd int, newfd int) (err error)
 //sys	EpollWait(epfd int, events []EpollEvent, msec int) (n int, err error)
 //sys	Fchown(fd int, uid int, gid int) (err error)
 //sys	Fstatfs(fd int, buf *Statfs_t) (err error)

unix/zsyscall_linux_mips64.go

@@ -1194,6 +1194,16 @@ func Munlockall() (err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func Dup2(oldfd int, newfd int) (err error) {
+	_, _, e1 := Syscall(SYS_DUP2, uintptr(oldfd), uintptr(newfd), 0)
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func EpollWait(epfd int, events []EpollEvent, msec int) (n int, err error) {
 	var _p0 unsafe.Pointer
 	if len(events) > 0 {

unix/zsyscall_linux_mips64le.go

@@ -1194,6 +1194,16 @@ func Munlockall() (err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func Dup2(oldfd int, newfd int) (err error) {
+	_, _, e1 := Syscall(SYS_DUP2, uintptr(oldfd), uintptr(newfd), 0)
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func EpollWait(epfd int, events []EpollEvent, msec int) (n int, err error) {
 	var _p0 unsafe.Pointer
 	if len(events) > 0 {