nt.spawnv doesn't properly escape quotes

[slozier]

test_cp15514 from Tests/modules/system_related/test_nt.py

import os, sys
cmd_cmd = os.path.join(os.environ["windir"], "system32", "cmd")
os.spawnv(os.P_WAIT, cmd_cmd , ["cmd", "/C", '""%s" -c "print(__name__)""' % sys.executable])

[slozier]

Same as IronLanguages/ironpython2#309.

Another example:

import os, sys
os.spawnv(0, sys.executable, [sys.executable, "-c", "assert True"])

CPython fails with a SyntaxError whereas we don't.