cmd/compile,go/types: restrict use of unsafe.{Add,Slice} to go1.17 or newer

This CL updates cmd/compile (including types2) and go/types to report
errors about using unsafe.Add and unsafe.Slice when language
compatibility is set to Go 1.16 or older.

Fixes #46525.

Change-Id: I1bfe025a672d9f4b929f443064ad1effd38d0363
Reviewed-on: https://go-review.googlesource.com/c/go/+/324369
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/test/fixedbugs/issue46525.go b/test/fixedbugs/issue46525.go
new file mode 100644
index 0000000000..164e1473ce
--- /dev/null
+++ b/test/fixedbugs/issue46525.go
@@ -0,0 +1,14 @@
+// errorcheck -lang=go1.16
+
+// Copyright 2021 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 p
+
+import "unsafe"
+
+func main() {
+	_ = unsafe.Add(unsafe.Pointer(nil), 0) // ERROR "unsafe.Add requires go1.17 or later"
+	_ = unsafe.Slice(new(byte), 1)         // ERROR "unsafe.Slice requires go1.17 or later"
+}