test: restore tests for the reject unsafe code option

Tests in test/safe were neglected after moving to the run.go
framework. This change restores them.

These tests are skipped for go/types via -+ option.

Fixes #25668

Change-Id: I8fe26574a76fa7afa8664c467d7c2e6334f1bba9
Reviewed-on: https://go-review.googlesource.com/124660
Reviewed-by: Brad Fitzpatrick <[email protected]>
Run-TryBot: Brad Fitzpatrick <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: Yury Smolsky

test/safe/main.go

@@ -0,0 +1,16 @@
+// errorcheck -u -+
+
+// 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.
+
+// Check that we cannot import a package that uses "unsafe" internally
+// when -u is supplied.
+
+package main
+
+import "syscall" // ERROR "import unsafe package"
+
+func main() {
+	print(syscall.Environ())
+}

test/safe/nousesafe.go

@@ -0,0 +1,15 @@
+// errorcheck -u -+
+
+// 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.
+
+// Check that we cannot import the "unsafe" package when -u is supplied.
+
+package a
+
+import "unsafe" // ERROR "import package unsafe"
+
+func Float32bits(f float32) uint32 {
+	return *(*uint32)(unsafe.Pointer(&f))
+}