unix: remove arch specific build for openbsd_pledge.go

The pledge code is platform specific, but in no way architecture specific.
As such, drop the +build rule that ties it to specific architectures.

While here also rename openbsd_pledge.go and openbsd_unveil.go so we can
drop the openbsd specific build tags.

Change-Id: I7d83796c8f9b46afe2a6790620205df5f7f3d738
Reviewed-on: https://go-review.googlesource.com/c/sys/+/173677
Reviewed-by: Elias Naur <mail@eliasnaur.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Elias Naur <mail@eliasnaur.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/unveil_openbsd.go

@@ -0,0 +1,42 @@
+// Copyright 2018 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.
+
+package unix
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+// Unveil implements the unveil syscall.
+// For more information see unveil(2).
+// Note that the special case of blocking further
+// unveil calls is handled by UnveilBlock.
+func Unveil(path string, flags string) error {
+	pathPtr, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return err
+	}
+	flagsPtr, err := syscall.BytePtrFromString(flags)
+	if err != nil {
+		return err
+	}
+	_, _, e := syscall.Syscall(SYS_UNVEIL, uintptr(unsafe.Pointer(pathPtr)), uintptr(unsafe.Pointer(flagsPtr)), 0)
+	if e != 0 {
+		return e
+	}
+	return nil
+}
+
+// UnveilBlock blocks future unveil calls.
+// For more information see unveil(2).
+func UnveilBlock() error {
+	// Both pointers must be nil.
+	var pathUnsafe, flagsUnsafe unsafe.Pointer
+	_, _, e := syscall.Syscall(SYS_UNVEIL, uintptr(pathUnsafe), uintptr(flagsUnsafe), 0)
+	if e != 0 {
+		return e
+	}
+	return nil
+}