Issue #12098: multiprocessing on Windows now starts child processes
  using the same sys.flags as the current process.
Backport from default branch.
diff --git a/Lib/multiprocessing/forking.py b/Lib/multiprocessing/forking.py
index 1597ae8..dc465b4 100644
--- a/Lib/multiprocessing/forking.py
+++ b/Lib/multiprocessing/forking.py
@@ -361,7 +361,8 @@
             return [sys.executable, '--multiprocessing-fork']
         else:
             prog = 'from multiprocessing.forking import main; main()'
-            return [_python_exe, '-c', prog, '--multiprocessing-fork']
+            opts = util._args_from_interpreter_flags()
+            return [_python_exe] + opts + ['-c', prog, '--multiprocessing-fork']
 
 
     def main():
diff --git a/Lib/multiprocessing/util.py b/Lib/multiprocessing/util.py
index fe76bcc..3ce480f 100644
--- a/Lib/multiprocessing/util.py
+++ b/Lib/multiprocessing/util.py
@@ -37,6 +37,7 @@
 import atexit
 import threading        # we want threading to install it's
                         # cleanup function before multiprocessing does
+from subprocess import _args_from_interpreter_flags
 
 from multiprocessing.process import current_process, active_children