"nogil" for C++ casts

--HG--
extra : transplant_source : %E0%C5%BDo%E6%D5GJ%92%14m%88%03%1C%B1%0B%1B%1B%98%C4

Cython/Includes/libcpp/cast.pxd

@@ -5,7 +5,7 @@
 # than the standard C cast operator which can be written "<T>(expression)" in
 # Cython.
 
-cdef extern from *:
+cdef extern from * nogil:
     cdef T dynamic_cast[T](void *) except +   # nullptr may also indicate failure
     cdef T static_cast[T](void *)
     cdef T reinterpret_cast[T](void *)