bpo-35134: Create Include/cpython/ subdirectory (GH-10624)

Include/*.h should be the "portable Python API", whereas
Include/cpython/*.h should be the "CPython API": CPython
implementation details.

Changes:

* Create Include/cpython/ subdirectory
* "make install" now creates $prefix/include/cpython and copy
  Include/cpython/* to $prefix/include/cpython
* Create Include/cpython/objimpl.h: move objimpl.h code
  surrounded by "#ifndef Py_LIMITED_API" to cpython/objimpl.h.
* objimpl.h now includes cpython/objimpl.h
* Windows installer (MSI) now also install Include/ subdirectories:
  Include/cpython/ and Include/internal/.
diff --git a/Include/cpython/objimpl.h b/Include/cpython/objimpl.h
new file mode 100644
index 0000000..f121922
--- /dev/null
+++ b/Include/cpython/objimpl.h
@@ -0,0 +1,113 @@
+#ifndef Py_CPYTHON_OBJIMPL_H
+#  error "this header file must not be included directly"
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* This function returns the number of allocated memory blocks, regardless of size */
+PyAPI_FUNC(Py_ssize_t) _Py_GetAllocatedBlocks(void);
+
+/* Macros */
+#ifdef WITH_PYMALLOC
+PyAPI_FUNC(int) _PyObject_DebugMallocStats(FILE *out);
+#endif
+
+
+typedef struct {
+    /* user context passed as the first argument to the 2 functions */
+    void *ctx;
+
+    /* allocate an arena of size bytes */
+    void* (*alloc) (void *ctx, size_t size);
+
+    /* free an arena */
+    void (*free) (void *ctx, void *ptr, size_t size);
+} PyObjectArenaAllocator;
+
+/* Get the arena allocator. */
+PyAPI_FUNC(void) PyObject_GetArenaAllocator(PyObjectArenaAllocator *allocator);
+
+/* Set the arena allocator. */
+PyAPI_FUNC(void) PyObject_SetArenaAllocator(PyObjectArenaAllocator *allocator);
+
+
+PyAPI_FUNC(Py_ssize_t) _PyGC_CollectNoFail(void);
+PyAPI_FUNC(Py_ssize_t) _PyGC_CollectIfEnabled(void);
+
+
+/* Test if an object has a GC head */
+#define PyObject_IS_GC(o) \
+    (PyType_IS_GC(Py_TYPE(o)) \
+     && (Py_TYPE(o)->tp_is_gc == NULL || Py_TYPE(o)->tp_is_gc(o)))
+
+/* GC information is stored BEFORE the object structure. */
+typedef struct {
+    // Pointer to next object in the list.
+    // 0 means the object is not tracked
+    uintptr_t _gc_next;
+
+    // Pointer to previous object in the list.
+    // Lowest two bits are used for flags documented later.
+    uintptr_t _gc_prev;
+} PyGC_Head;
+
+#define _Py_AS_GC(o) ((PyGC_Head *)(o)-1)
+
+/* True if the object is currently tracked by the GC. */
+#define _PyObject_GC_IS_TRACKED(o) (_Py_AS_GC(o)->_gc_next != 0)
+
+/* True if the object may be tracked by the GC in the future, or already is.
+   This can be useful to implement some optimizations. */
+#define _PyObject_GC_MAY_BE_TRACKED(obj) \
+    (PyObject_IS_GC(obj) && \
+        (!PyTuple_CheckExact(obj) || _PyObject_GC_IS_TRACKED(obj)))
+
+
+/* Bit flags for _gc_prev */
+/* Bit 0 is set when tp_finalize is called */
+#define _PyGC_PREV_MASK_FINALIZED  (1)
+/* Bit 1 is set when the object is in generation which is GCed currently. */
+#define _PyGC_PREV_MASK_COLLECTING (2)
+/* The (N-2) most significant bits contain the real address. */
+#define _PyGC_PREV_SHIFT           (2)
+#define _PyGC_PREV_MASK            (((uintptr_t) -1) << _PyGC_PREV_SHIFT)
+
+// Lowest bit of _gc_next is used for flags only in GC.
+// But it is always 0 for normal code.
+#define _PyGCHead_NEXT(g)        ((PyGC_Head*)(g)->_gc_next)
+#define _PyGCHead_SET_NEXT(g, p) ((g)->_gc_next = (uintptr_t)(p))
+
+// Lowest two bits of _gc_prev is used for _PyGC_PREV_MASK_* flags.
+#define _PyGCHead_PREV(g) ((PyGC_Head*)((g)->_gc_prev & _PyGC_PREV_MASK))
+#define _PyGCHead_SET_PREV(g, p) do { \
+    assert(((uintptr_t)p & ~_PyGC_PREV_MASK) == 0); \
+    (g)->_gc_prev = ((g)->_gc_prev & ~_PyGC_PREV_MASK) \
+        | ((uintptr_t)(p)); \
+    } while (0)
+
+#define _PyGCHead_FINALIZED(g) \
+    (((g)->_gc_prev & _PyGC_PREV_MASK_FINALIZED) != 0)
+#define _PyGCHead_SET_FINALIZED(g) \
+    ((g)->_gc_prev |= _PyGC_PREV_MASK_FINALIZED)
+
+#define _PyGC_FINALIZED(o) \
+    _PyGCHead_FINALIZED(_Py_AS_GC(o))
+#define _PyGC_SET_FINALIZED(o) \
+    _PyGCHead_SET_FINALIZED(_Py_AS_GC(o))
+
+
+PyAPI_FUNC(PyObject *) _PyObject_GC_Malloc(size_t size);
+PyAPI_FUNC(PyObject *) _PyObject_GC_Calloc(size_t size);
+
+
+/* Test if a type supports weak references */
+#define PyType_SUPPORTS_WEAKREFS(t) ((t)->tp_weaklistoffset > 0)
+
+#define PyObject_GET_WEAKREFS_LISTPTR(o) \
+    ((PyObject **) (((char *) (o)) + Py_TYPE(o)->tp_weaklistoffset))
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/Include/objimpl.h b/Include/objimpl.h
index aee3fdc..f475ed0 100644
--- a/Include/objimpl.h
+++ b/Include/objimpl.h
@@ -101,17 +101,6 @@
 PyAPI_FUNC(void *) PyObject_Realloc(void *ptr, size_t new_size);
 PyAPI_FUNC(void) PyObject_Free(void *ptr);
 
-#ifndef Py_LIMITED_API
-/* This function returns the number of allocated memory blocks, regardless of size */
-PyAPI_FUNC(Py_ssize_t) _Py_GetAllocatedBlocks(void);
-#endif /* !Py_LIMITED_API */
-
-/* Macros */
-#ifdef WITH_PYMALLOC
-#ifndef Py_LIMITED_API
-PyAPI_FUNC(int) _PyObject_DebugMallocStats(FILE *out);
-#endif /* #ifndef Py_LIMITED_API */
-#endif
 
 /* Macros */
 #define PyObject_MALLOC         PyObject_Malloc
@@ -226,24 +215,6 @@
    constructor you would start directly with PyObject_Init/InitVar
 */
 
-#ifndef Py_LIMITED_API
-typedef struct {
-    /* user context passed as the first argument to the 2 functions */
-    void *ctx;
-
-    /* allocate an arena of size bytes */
-    void* (*alloc) (void *ctx, size_t size);
-
-    /* free an arena */
-    void (*free) (void *ctx, void *ptr, size_t size);
-} PyObjectArenaAllocator;
-
-/* Get the arena allocator. */
-PyAPI_FUNC(void) PyObject_GetArenaAllocator(PyObjectArenaAllocator *allocator);
-
-/* Set the arena allocator. */
-PyAPI_FUNC(void) PyObject_SetArenaAllocator(PyObjectArenaAllocator *allocator);
-#endif
 
 
 /*
@@ -254,11 +225,6 @@
 /* C equivalent of gc.collect() which ignores the state of gc.enabled. */
 PyAPI_FUNC(Py_ssize_t) PyGC_Collect(void);
 
-#ifndef Py_LIMITED_API
-PyAPI_FUNC(Py_ssize_t) _PyGC_CollectNoFail(void);
-PyAPI_FUNC(Py_ssize_t) _PyGC_CollectIfEnabled(void);
-#endif
-
 /* Test if a type has a GC head */
 #define PyType_IS_GC(t) PyType_HasFeature((t), Py_TPFLAGS_HAVE_GC)
 
@@ -267,72 +233,7 @@
                 ( (type *) _PyObject_GC_Resize(_PyVarObject_CAST(op), (n)) )
 
 
-#ifndef Py_LIMITED_API
-/* Test if an object has a GC head */
-#define PyObject_IS_GC(o) \
-    (PyType_IS_GC(Py_TYPE(o)) \
-     && (Py_TYPE(o)->tp_is_gc == NULL || Py_TYPE(o)->tp_is_gc(o)))
 
-/* GC information is stored BEFORE the object structure. */
-typedef struct {
-    // Pointer to next object in the list.
-    // 0 means the object is not tracked
-    uintptr_t _gc_next;
-
-    // Pointer to previous object in the list.
-    // Lowest two bits are used for flags documented later.
-    uintptr_t _gc_prev;
-} PyGC_Head;
-
-#define _Py_AS_GC(o) ((PyGC_Head *)(o)-1)
-
-/* True if the object is currently tracked by the GC. */
-#define _PyObject_GC_IS_TRACKED(o) (_Py_AS_GC(o)->_gc_next != 0)
-
-/* True if the object may be tracked by the GC in the future, or already is.
-   This can be useful to implement some optimizations. */
-#define _PyObject_GC_MAY_BE_TRACKED(obj) \
-    (PyObject_IS_GC(obj) && \
-        (!PyTuple_CheckExact(obj) || _PyObject_GC_IS_TRACKED(obj)))
-
-
-/* Bit flags for _gc_prev */
-/* Bit 0 is set when tp_finalize is called */
-#define _PyGC_PREV_MASK_FINALIZED  (1)
-/* Bit 1 is set when the object is in generation which is GCed currently. */
-#define _PyGC_PREV_MASK_COLLECTING (2)
-/* The (N-2) most significant bits contain the real address. */
-#define _PyGC_PREV_SHIFT           (2)
-#define _PyGC_PREV_MASK            (((uintptr_t) -1) << _PyGC_PREV_SHIFT)
-
-// Lowest bit of _gc_next is used for flags only in GC.
-// But it is always 0 for normal code.
-#define _PyGCHead_NEXT(g)        ((PyGC_Head*)(g)->_gc_next)
-#define _PyGCHead_SET_NEXT(g, p) ((g)->_gc_next = (uintptr_t)(p))
-
-// Lowest two bits of _gc_prev is used for _PyGC_PREV_MASK_* flags.
-#define _PyGCHead_PREV(g) ((PyGC_Head*)((g)->_gc_prev & _PyGC_PREV_MASK))
-#define _PyGCHead_SET_PREV(g, p) do { \
-    assert(((uintptr_t)p & ~_PyGC_PREV_MASK) == 0); \
-    (g)->_gc_prev = ((g)->_gc_prev & ~_PyGC_PREV_MASK) \
-        | ((uintptr_t)(p)); \
-    } while (0)
-
-#define _PyGCHead_FINALIZED(g) \
-    (((g)->_gc_prev & _PyGC_PREV_MASK_FINALIZED) != 0)
-#define _PyGCHead_SET_FINALIZED(g) \
-    ((g)->_gc_prev |= _PyGC_PREV_MASK_FINALIZED)
-
-#define _PyGC_FINALIZED(o) \
-    _PyGCHead_FINALIZED(_Py_AS_GC(o))
-#define _PyGC_SET_FINALIZED(o) \
-    _PyGCHead_SET_FINALIZED(_Py_AS_GC(o))
-#endif   /* !defined(Py_LIMITED_API) */
-
-#ifndef Py_LIMITED_API
-PyAPI_FUNC(PyObject *) _PyObject_GC_Malloc(size_t size);
-PyAPI_FUNC(PyObject *) _PyObject_GC_Calloc(size_t size);
-#endif /* !Py_LIMITED_API */
 PyAPI_FUNC(PyObject *) _PyObject_GC_New(PyTypeObject *);
 PyAPI_FUNC(PyVarObject *) _PyObject_GC_NewVar(PyTypeObject *, Py_ssize_t);
 
@@ -368,13 +269,10 @@
         }                                                               \
     } while (0)
 
-
-/* Test if a type supports weak references */
 #ifndef Py_LIMITED_API
-#define PyType_SUPPORTS_WEAKREFS(t) ((t)->tp_weaklistoffset > 0)
-
-#define PyObject_GET_WEAKREFS_LISTPTR(o) \
-    ((PyObject **) (((char *) (o)) + Py_TYPE(o)->tp_weaklistoffset))
+#  define Py_CPYTHON_OBJIMPL_H
+#  include  "cpython/objimpl.h"
+#  undef Py_CPYTHON_OBJIMPL_H
 #endif
 
 #ifdef __cplusplus