[3.12] gh-112536: Define `_Py_THREAD_SANITIZER` on GCC when TSan is enabled (GH-117702) (#117713)

gh-112536: Define `_Py_THREAD_SANITIZER` on GCC when TSan is enabled (GH-117702)

The `__has_feature(thread_sanitizer)` is a Clang-ism. Although new
versions of GCC implement `__has_feature`, the `defined(__has_feature)`
check still fails on GCC so we don't use that code path.
(cherry picked from commit 79eec66e3dc277ea6ebad8c0b33756eea6a7ab3b)

Co-authored-by: Sam Gross <colesbury@gmail.com>