shutil.copytree(symlinks=True) fails when copying symlinks cross-device and there is no alternative

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-02-09.21:12:34.636>
labels = ['3.7', 'type-bug', 'library']
title = 'shutil.copytree(symlinks=True) fails when copying symlinks cross-device and there is no alternative'
updated_at = <Date 2018-07-11.07:46:05.806>
user = 'https://github.com/darko-poljak'

bugs.python.org fields:

activity = <Date 2018-07-11.07:46:05.806>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2017-02-09.21:12:34.636>
creator = 'poljakowski'
dependencies = []
files = []
hgrepos = []
issue_num = 29516
keywords = []
message_count = 1.0
messages = ['287455']
nosy_count = 1.0
nosy_names = ['poljakowski']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue29516'
versions = ['Python 3.3', 'Python 3.4', 'Python 3.5', 'Python 3.6', 'Python 3.7']