setup_helpers: try import multiprocessing.synchronize too

Author: jbarlow83

pybind11/setup_helpers.py

@@ -411,6 +411,9 @@ def _single_compile(obj):
 
             try:
                 import multiprocessing
+                import multiprocessing.synchronize  # Check for platforms like that have some
+                                                    # multiprocess capabilities but lack semaphores,
+                                                    # such as AWS Lambda and Android Termux.
                 from multiprocessing.pool import ThreadPool
             except ImportError:
                 threads = 1