syscall: use 32-bit setuid/setgid syscalls on linux/{386,arm}

Fixes #17092

Change-Id: Ib14e4db13116ebbe4d72c414fb979d27a06d6174
Reviewed-on: https://go-review.googlesource.com/33011
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/syscall/exec_linux.go

@@ -219,11 +219,11 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 				goto childerror
 			}
 		}
-		_, _, err1 = RawSyscall(SYS_SETGID, uintptr(cred.Gid), 0, 0)
+		_, _, err1 = RawSyscall(sys_SETGID, uintptr(cred.Gid), 0, 0)
 		if err1 != 0 {
 			goto childerror
 		}
-		_, _, err1 = RawSyscall(SYS_SETUID, uintptr(cred.Uid), 0, 0)
+		_, _, err1 = RawSyscall(sys_SETUID, uintptr(cred.Uid), 0, 0)
 		if err1 != 0 {
 			goto childerror
 		}

src/syscall/setuidgid_32_linux.go

+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build linux
+// +build 386 arm
+
+package syscall
+
+const (
+	sys_SETGID = SYS_SETGID32
+	sys_SETUID = SYS_SETUID32
+)

src/syscall/setuidgid_linux.go

+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build linux
+// +build !386,!arm
+
+package syscall
+
+const (
+	sys_SETGID = SYS_SETGID
+	sys_SETUID = SYS_SETUID
+)