pythongh-112536: Define _Py_THREAD_SANITIZER on GCC when TSan is enabled (pythonGH-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 79eec66)

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

Author: colesbury

Include/pyport.h

@@ -757,6 +757,9 @@ extern char * _getpty(int *, int, mode_t, int);
 #  if defined(__SANITIZE_ADDRESS__)
 #    define _Py_ADDRESS_SANITIZER
 #  endif
+#  if defined(__SANITIZE_THREAD__)
+#    define _Py_THREAD_SANITIZER
+#  endif
 #endif