[clang] [Clang][NFC] Refactor `Targets.h` to make it publicly accessible (PR #116090)

[Bruno Cardoso Lopes via cfe-commits]

================
@@ -0,0 +1,39 @@
+//===------- TargetDefines.h - Target define helpers ------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares a series of helper functions for defining target-specific
+// macros.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_LIB_BASIC_TARGETDEFINES_H
+#define LLVM_CLANG_LIB_BASIC_TARGETDEFINES_H
+
+#include "clang/Basic/LangOptions.h"
+#include "clang/Basic/MacroBuilder.h"
+#include "llvm/ADT/StringRef.h"
+
+namespace clang {
+namespace targets {
+/// DefineStd - Define a macro name and standard variants.  For example if
----------------
bcardosolopes wrote:

Since you are moving, perhaps remove the `DefineStd - ` in the comments.

https://github.com/llvm/llvm-project/pull/116090