setup.py fails with UnicodeDecodeError

[John W. O'Brien]

When Python's default encoding, which is environment-dependent, is 'ascii', setup.py will fail with

UnicodeDecodeError: 'ascii' codec can't decode byte 0xc4 in position 184: ordinal not in range(128)

This affects, for example, building the devel/py-arpeggio port against Python 3.6 on FreeBSD 12.2 with poudriere.