Introduce an indirection header for including Python.h.

We should no longer include Python.h directly and instead use the new
pySafePython.h file. Including Python.h directly is known to cause
problems on certain platforms with certain build configurations.

A follow up change will replace all current includes of Python.h.

See #785
See #1006

(Internal change: 2033910)

pxr/base/tf/CMakeLists.txt

@@ -137,6 +137,7 @@ pxr_library(tf
  type_Impl.h
 
  PYTHON_PUBLIC_HEADERS
+ pySafePython.h
  pyStaticTokens.h
 
  PRIVATE_CLASSES

pxr/base/tf/pySafePython.h

@@ -0,0 +1,34 @@
+//
+// Copyright 2020 Pixar
+//
+// Licensed under the Apache License, Version 2.0 (the "Apache License")
+// with the following modification; you may not use this file except in
+// compliance with the Apache License and the following modification to it:
+// Section 6. Trademarks. is deleted and replaced with:
+//
+// 6. Trademarks. This License does not grant permission to use the trade
+// names, trademarks, service marks, or product names of the Licensor
+// and its affiliates, except as required to comply with Section 4(c) of
+// the License and to reproduce the content of the NOTICE file.
+//
+// You may obtain a copy of the Apache License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the Apache License with the above modification is
+// distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the Apache License for the specific
+// language governing permissions and limitations under the Apache License.
+//
+#ifndef PXR_BASE_TF_PY_SAFE_PYTHON_H
+#define PXR_BASE_TF_PY_SAFE_PYTHON_H
+
+/// \file tf/pySafePython.h
+/// Intended to replace a direct include of Python.h, which causes several
+/// build problems with certain configurations and platforms (e.g., debug 
+/// builds on Windows)
+
+#include <boost/python/detail/wrap_python.hpp>
+
+#endif // PXR_BASE_TF_PY_SAFE_PYTHON_H