Fix ARM64 build.

The common syscall definitions mean that ARM64-exclusive files need stubs in
the ARM64 build.

PiperOrigin-RevId: 310446698

pkg/sentry/syscalls/linux/BUILD

@@ -49,7 +49,8 @@ go_library(
         "sys_time.go",
         "sys_timer.go",
         "sys_timerfd.go",
-        "sys_tls.go",
+        "sys_tls_amd64.go",
+        "sys_tls_arm64.go",
         "sys_utsname.go",
         "sys_write.go",
         "sys_xattr.go",

pkg/sentry/syscalls/linux/sys_tls_arm64.go

@@ -0,0 +1,28 @@
+// Copyright 2018 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//+build arm64
+
+package linux
+
+import (
+	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+// ArchPrctl is not defined for ARM64.
+func ArchPrctl(*kernel.Task, arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	return 0, nil, syserror.ENOSYS
+}

pkg/sentry/syscalls/linux/sys_utsname.go

@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// +build amd64 arm64
-
 package linux
 
 import (