bpo-35177: Add dependencies between header files (GH-10361)

* ast.h now includes Python-ast.h and node.h
* parsetok.h now includes node.h and grammar.h
* symtable.h now includes Python-ast.h
* Modify asdl_c.py to enhance Python-ast.h:

  * Add #ifndef/#define Py_PYTHON_AST_H to be able to include the header
    twice
  * Add "extern { ... }" for C++
  * Undefine "Yield" macro conflicting with winbase.h

* Remove "#undef Yield" from C files, it's now done in Python-ast.h
* Remove now useless includes in C files

Include/Python-ast.h

@@ -1,7 +1,15 @@
 /* File automatically generated by Parser/asdl_c.py. */
 
+#ifndef Py_PYTHON_AST_H
+#define Py_PYTHON_AST_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #include "asdl.h"
 
+#undef Yield /* undefine macro conflicting with winbase.h */
+
 typedef struct _mod *mod_ty;
 
 typedef struct _stmt *stmt_ty;
@@ -607,3 +615,8 @@ withitem_ty _Py_withitem(expr_ty context_expr, expr_ty optional_vars, PyArena
 PyObject* PyAST_mod2obj(mod_ty t);
 mod_ty PyAST_obj2mod(PyObject* ast, PyArena* arena, int mode);
 int PyAST_Check(PyObject* obj);
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_PYTHON_AST_H */