gh-112536: Define _Py_THREAD_SANITIZER on GCC when TSan is enabled (#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.

Author: colesbury

Include/pyport.h

@@ -572,6 +572,9 @@ extern "C" {
 #  if defined(__SANITIZE_ADDRESS__)
 #    define _Py_ADDRESS_SANITIZER
 #  endif
+#  if defined(__SANITIZE_THREAD__)
+#    define _Py_THREAD_SANITIZER
+#  endif
 #endif