[3.12] gh-129838: Don't redefine _Py_NO_SANITIZE_UNDEFINED (GH-129839) (#130365)

gh-129838: Don't redefine _Py_NO_SANITIZE_UNDEFINED (GH-129839)

Newer GCC versions accept both __attribute__((no_sanitize("undefined")))
and __attribute__((no_sanitize_undefined)) so check that the macro is
not already defined.
(cherry picked from commit 568db400ff07240a5ed6f263af281405ccaec716)

Co-authored-by: Collin Funk <collin.funk1@gmail.com>