Building a C extension on Big Sur and SDK v10.15 fails

GitHub fields:

assignee = 'https://github.com/ned-deily'
closed_at = None
created_at = <Date 2021-06-23.00:52:48.311>
labels = ['OS-mac', 'type-bug', 'library', '3.10']
title = 'Building a C extension on Big Sur and SDK v10.15 fails'
updated_at = <Date 2021-09-09.20:19:46.021>
user = 'https://bugs.python.org/philthompson10'

bugs.python.org fields:

activity = <Date 2021-09-09.20:19:46.021>
actor = 'ned.deily'
assignee = 'ned.deily'
closed = False
closed_date = None
closer = None
components = ['Distutils', 'macOS']
creation = <Date 2021-06-23.00:52:48.311>
creator = 'philthompson10'
dependencies = []
files = []
hgrepos = []
issue_num = 44492
keywords = []
message_count = 3.0
messages = ['396377', '396388', '401473']
nosy_count = 5.0
nosy_names = ['ronaldoussoren', 'philthompson10', 'ned.deily', 'eric.araujo', 'dstufft']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue44492'
versions = ['Python 3.10']