merge 68874 to py3kwq!
diff --git a/setup.py b/setup.py
index 27d1fe1..174a8b2 100644
--- a/setup.py
+++ b/setup.py
@@ -1063,9 +1063,12 @@
             if macros.get('HAVE_SEM_OPEN', False):
                 multiprocessing_srcs.append('_multiprocessing/semaphore.c')
 
-        exts.append ( Extension('_multiprocessing', multiprocessing_srcs,
-                                 define_macros=list(macros.items()),
-                                 include_dirs=["Modules/_multiprocessing"]))
+        if sysconfig.get_config_var('WITH_THREAD'):
+            exts.append ( Extension('_multiprocessing', multiprocessing_srcs,
+                                    define_macros=list(macros.items()),
+                                    include_dirs=["Modules/_multiprocessing"]))
+        else:
+            missing.append('_multiprocessing')
         # End multiprocessing
 
         # Platform-specific libraries