Fix std::pointer_safety type in ABI v2

In the C++ standard `std::pointer_safety` is defined
as a C++11 strongly typed enum. However libc++ currently defines
it as a class type which simulates a C++11 enumeration. This
can be detected in valid C++ code.

This patch introduces an the _LIBCPP_ABI_POINTER_SAFETY_ENUM_TYPE ABI option.
When defined `std::pointer_safety` is implemented as an enum type.
Unfortunatly this also means it can no longer be provided as an extension
in C++03.

Additionally this patch moves the definition for `get_pointer_safety()`
out of the dylib, and into the headers. New usages of `get_pointer_safety()`
will now use the inline version instead of the dylib version. However in
order to keep the dylib ABI compatible the old definition is explicitly
compiled into it.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@291046 91177308-0d34-0410-b5e6-96231b3b80d8

test/libcxx/utilities/memory/util.dynamic.safety/get_pointer_safety_cxx03.pass.cpp

@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <memory>
+
+// pointer_safety get_pointer_safety();
+
+#include <memory>
+#include <cassert>
+
+int main()
+{
+  // Test that std::pointer_safety is still offered in C++03 under the old ABI.
+#ifndef _LIBCPP_ABI_POINTER_SAFETY_ENUM_TYPE
+    std::pointer_safety r = std::get_pointer_safety();
+    assert(r == std::pointer_safety::relaxed ||
+           r == std::pointer_safety::preferred ||
+           r == std::pointer_safety::strict);
+#endif
+}

test/libcxx/utilities/memory/util.dynamic.safety/get_pointer_safety_new_abi.pass.cpp

@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <memory>
+
+// pointer_safety get_pointer_safety();
+
+// The pointer_safety interface is no longer provided in C++03 in the new ABI.
+// XFAIL: c++98, c++03
+
+// MODULES_DEFINES: _LIBCPP_ABI_POINTER_SAFETY_ENUM_TYPE
+#define _LIBCPP_ABI_POINTER_SAFETY_ENUM_TYPE
+#include <memory>
+#include <cassert>
+
+int main()
+{
+  {
+    static_assert(std::is_enum<std::pointer_safety>::value, "");
+    static_assert(!std::is_convertible<std::pointer_safety, int>::value, "");
+    static_assert(std::is_same<
+        std::underlying_type<std::pointer_safety>::type,
+        unsigned char
+    >::value, "");
+  }
+  {
+    std::pointer_safety r = std::get_pointer_safety();
+    assert(r == std::pointer_safety::relaxed ||
+           r == std::pointer_safety::preferred ||
+           r == std::pointer_safety::strict);
+  }
+}