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/parsetok.h

@@ -1,5 +1,5 @@
-
 /* Parser-tokenizer link interface */
+
 #ifndef Py_LIMITED_API
 #ifndef Py_PARSETOK_H
 #define Py_PARSETOK_H
@@ -7,6 +7,9 @@
 extern "C" {
 #endif
 
+#include "grammar.h"      /* grammar */
+#include "node.h"         /* node */
+
 typedef struct {
     int error;
 #ifndef PGEN