Allow cross compiling python for macos-arm64 from macos-x86_64

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-11-26.18:52:40.601>
labels = ['OS-mac', 'build', '3.8', '3.9', '3.10', 'type-feature']
title = 'Allow cross compiling python for macos-arm64 from macos-x86_64'
updated_at = <Date 2020-11-26.20:18:03.658>
user = 'https://github.com/isuruf'

bugs.python.org fields:

activity = <Date 2020-11-26.20:18:03.658>
actor = 'ronaldoussoren'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Build', 'macOS']
creation = <Date 2020-11-26.18:52:40.601>
creator = 'isuruf'
dependencies = []
files = []
hgrepos = []
issue_num = 42476
keywords = ['patch']
message_count = 2.0
messages = ['381908', '381913']
nosy_count = 4.0
nosy_names = ['ronaldoussoren', 'ned.deily', 'willingc', 'isuruf']
pr_nums = ['23523']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue42476'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']