Fallback to dev_urandom doesn't work when py_getrandom returns -1

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2018-01-17.13:11:08.071>
labels = ['build']
title = "Fallback to dev_urandom doesn't work when py_getrandom returns -1"
updated_at = <Date 2018-01-17.20:52:10.985>
user = 'https://github.com/jernejs'

bugs.python.org fields:

activity = <Date 2018-01-17.20:52:10.985>
actor = 'jernejs'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Build']
creation = <Date 2018-01-17.13:11:08.071>
creator = 'jernejs'
dependencies = []
files = ['47389']
hgrepos = []
issue_num = 32580
keywords = ['patch']
message_count = 5.0
messages = ['310158', '310162', '310196', '310197', '310206']
nosy_count = 2.0
nosy_names = ['vstinner', 'jernejs']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue32580'
versions = ['Python 3.5', 'Python 3.6']