[3.13] gh-141370: document undefined behavior of Py_ABS() (GH-141439) (GH-141455)

(cherry picked from commit 20f53df)

Co-authored-by: Sergey B Kirpichev <[email protected]>

Author: miss-islington

Doc/c-api/intro.rst

@@ -133,6 +133,10 @@ complete listing.
 
    Return the absolute value of ``x``.
 
+   If the result cannot be represented (for example, if ``x`` has
+   :c:macro:`!INT_MIN` value for :c:expr:`int` type), the behavior is
+   undefined.
+
    .. versionadded:: 3.3
 
 .. c:macro:: Py_ALWAYS_INLINE