Add TSS (Thread Specific Storage) API in CPython 3.7+

Cython/Includes/cpython/pythread.pxd

@@ -29,7 +29,7 @@ cdef extern from "pythread.h":
     size_t PyThread_get_stacksize()
     int PyThread_set_stacksize(size_t)
 
-    # Thread Local Storage (TLS) API
+    # Thread Local Storage (TLS) API deprecated in CPython 3.7+
     int PyThread_create_key()
     void PyThread_delete_key(int)
     int PyThread_set_key_value(int, void *)
@@ -38,3 +38,15 @@ cdef extern from "pythread.h":
 
     # Cleanup after a fork
     void PyThread_ReInitTLS()
+
+    # Thread Specific Storage (TSS) API in CPython 3.7+
+    ctypedef struct Py_tss_t:
+        pass
+    Py_tss_t Py_tss_NEEDS_INIT
+    Py_tss_t * PyThread_tss_alloc()
+    void PyThread_tss_free(Py_tss_t *key)
+    int PyThread_tss_is_created(Py_tss_t *key)
+    int PyThread_tss_create(Py_tss_t *key)
+    void PyThread_tss_delete(Py_tss_t *key)
+    int PyThread_tss_set(Py_tss_t *key, void *value)
+    void * PyThread_tss_get(Py_tss_t *key)