syscall: use Getpgid to emulate Getpgrp on linux

Fixes newly introduced test on linux/arm64 because linux/arm64 doesn't
have the getpgrp syscall. Getpgid(0) is documented to be equivalent to
Getpgrp.

Change-Id: I8f30f4f8de8c32fe04a29c9c4a9330d4e4e6b46d
Signed-off-by: Shenghou Ma <minux@golang.org>
Reviewed-on: https://go-review.googlesource.com/8022Reviewed-by: Aram Hăvărneanu <aram@mgk.ro>
Reviewed-by: Rob Pike <r@golang.org>

src/syscall/syscall_linux.go

@@ -839,7 +839,12 @@ func Mount(source string, target string, fstype string, flags uintptr, data stri
 //sys	Fsync(fd int) (err error)
 //sys	Getdents(fd int, buf []byte) (n int, err error) = SYS_GETDENTS64
 //sysnb	Getpgid(pid int) (pgid int, err error)
-//sysnb	Getpgrp() (pid int)
+
+func Getpgrp() (pid int) {
+	pid, _ = Getpgid(0)
+	return
+}
+
 //sysnb	Getpid() (pid int)
 //sysnb	Getppid() (ppid int)
 //sys	Getpriority(which int, who int) (prio int, err error)

src/syscall/zsyscall_linux_386.go

@@ -524,14 +524,6 @@ func Getpgid(pid int) (pgid int, err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Getpgrp() (pid int) {
-	r0, _, _ := RawSyscall(SYS_GETPGRP, 0, 0, 0)
-	pid = int(r0)
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Getpid() (pid int) {
 	r0, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0)
 	pid = int(r0)

src/syscall/zsyscall_linux_amd64.go

@@ -524,14 +524,6 @@ func Getpgid(pid int) (pgid int, err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Getpgrp() (pid int) {
-	r0, _, _ := RawSyscall(SYS_GETPGRP, 0, 0, 0)
-	pid = int(r0)
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Getpid() (pid int) {
 	r0, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0)
 	pid = int(r0)

src/syscall/zsyscall_linux_arm.go

@@ -524,14 +524,6 @@ func Getpgid(pid int) (pgid int, err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Getpgrp() (pid int) {
-	r0, _, _ := RawSyscall(SYS_GETPGRP, 0, 0, 0)
-	pid = int(r0)
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Getpid() (pid int) {
 	r0, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0)
 	pid = int(r0)

src/syscall/zsyscall_linux_arm64.go

@@ -524,14 +524,6 @@ func Getpgid(pid int) (pgid int, err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Getpgrp() (pid int) {
-	r0, _, _ := RawSyscall(SYS_GETPGRP, 0, 0, 0)
-	pid = int(r0)
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Getpid() (pid int) {
 	r0, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0)
 	pid = int(r0)

src/syscall/zsyscall_linux_ppc64.go

@@ -524,14 +524,6 @@ func Getpgid(pid int) (pgid int, err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Getpgrp() (pid int) {
-	r0, _, _ := RawSyscall(SYS_GETPGRP, 0, 0, 0)
-	pid = int(r0)
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Getpid() (pid int) {
 	r0, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0)
 	pid = int(r0)

src/syscall/zsyscall_linux_ppc64le.go

@@ -524,14 +524,6 @@ func Getpgid(pid int) (pgid int, err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Getpgrp() (pid int) {
-	r0, _, _ := RawSyscall(SYS_GETPGRP, 0, 0, 0)
-	pid = int(r0)
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Getpid() (pid int) {
 	r0, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0)
 	pid = int(r0)