subprocess.Popen does not work on Linux

[slozier]

Traceback (most recent call last):
  File "Tests/modules/io_related/test_codecs.py", line 526, in <module>
  File "/mnt/r/Documents/Programming-github/ironpython3/bin/Debug/net45/Lib/iptest/ipunittest.py", line 356, in run_test
  File "/mnt/r/Documents/Programming-github/ironpython3/Src/StdLib/Lib/test/support/__init__.py", line 1817, in run_unittest
  File "/mnt/r/Documents/Programming-github/ironpython3/Src/StdLib/Lib/test/support/__init__.py", line 1792, in _run_suite
test.support.TestFailed: Traceback (most recent call last):
  File "Tests/modules/io_related/test_codecs.py", line 382, in test_cp11334
    p = subprocess.Popen([sys.executable, os.path.join(self.test_dir, "encoded_files", "cp11334_warn.py")], shell=True, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
  File "/mnt/r/Documents/Programming-github/ironpython3/Src/StdLib/Lib/subprocess.py", line 850, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/mnt/r/Documents/Programming-github/ironpython3/Src/StdLib/Lib/subprocess.py", line 1396, in _execute_child
    self.pid = _posixsubprocess.fork_exec(
NotImplementedError: fork_exec is currently not implemented