identify cross builds by a more generic environment setting.

GitHub fields:

assignee = 'https://github.com/doko42'
closed_at = None
created_at = <Date 2016-09-13.10:53:53.699>
labels = ['type-bug', 'build']
title = 'identify cross builds by a more generic environment setting.'
updated_at = <Date 2019-12-10.08:14:17.013>
user = 'https://github.com/doko42'

bugs.python.org fields:

activity = <Date 2019-12-10.08:14:17.013>
actor = 'xdegaye'
assignee = 'doko'
closed = False
closed_date = None
closer = None
components = ['Cross-Build']
creation = <Date 2016-09-13.10:53:53.699>
creator = 'doko'
dependencies = []
files = []
hgrepos = []
issue_num = 28125
keywords = []
message_count = 9.0
messages = ['276244', '276279', '276342', '276349', '276351', '276357', '276361', '276438', '276440']
nosy_count = 5.0
nosy_names = ['doko', 'vstinner', 'zach.ware', 'Alex.Willmer', 'yan12125']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue28125'
versions = ['Python 3.6']