bpo-37160: Thread native ID NetBSD support (GH-13835)

diff --git a/Python/thread_pthread.h b/Python/thread_pthread.h
index 740b521..9b4b23b 100644
--- a/Python/thread_pthread.h
+++ b/Python/thread_pthread.h
@@ -18,6 +18,8 @@
 #   include <pthread_np.h>      /* pthread_getthreadid_np() */
 #elif defined(__OpenBSD__)
 #   include <unistd.h>          /* getthrid() */
+#elif defined(__NetBSD__)       /* _lwp_self */
+#   include <lwp.h>
 #endif
 
 /* The POSIX spec requires that use of pthread_attr_setstacksize
@@ -328,6 +330,9 @@
 #elif defined(__OpenBSD__)
     pid_t native_id;
     native_id = getthrid();
+#elif defined(__NetBSD__)
+    lwpid_t native_id;
+    native_id = _lwp_self();
 #endif
     return (unsigned long) native_id;
 }