Log Message:
math/py-scipy12: Work around mac extraction woes

On macOS 10.13 (at least), unpacking the distfile as root results in
files that have strange permissions, including group/world writable
and executable.  The upstream distfile has these, but extracting on
other systems or on mac not as root applies some sort of umask.  On
Darwin only, chmod these spurious bits away.  Tested to work as
non-root and root on macOS 10.13, and by inspection will not affect
!macOS.