Avoid mixing declarations and code in the C API to fix the compiler
warning: "ISO C90 forbids mixed declarations and code"
[-Werror=declaration-after-statement].
Convert the following macros to static inline functions:
* PyCell_GET()
* PyCell_SET()
Limited C API version 3.12 no longer casts arguments.
Fix also usage of PyCell_SET(): only delete the old value after
setting the new value.
Add a new _Py_RVALUE() macro to prevent using an expression as an
l-value.
Replace a "(void)" cast with the _Py_RVALUE() macro in the following
macros:
* PyCell_SET()
* PyList_SET_ITEM()
* PyTuple_SET_ITEM()
* _PyGCHead_SET_FINALIZED()
* _PyGCHead_SET_NEXT()
* asdl_seq_SET()
* asdl_seq_SET_UNTYPED()
Add also parentheses around macro arguments in PyCell_SET() and
PyTuple_SET_ITEM() macros.
