audio/cdparanoia: make the port more robust against exotic machines

The port comes with rather old pregenerated GNU autoconf bits which
are unaware of the modern machine architectures, e.g. aarch64 et al.
Previous (even older) version would emit a warning but continue the
configure process; now this is hard error. Additionally, configure
script copies its own config.{guess,sub} files over the ones coming
from our templates. This is easy to untangle, but if done properly,
would require to rebootstrap the whole thing (USES+=autoreconf).

Instead, simply extend the existing *-unknown fallback to treat any
unmatched *-portbld system type similarly (i.e., gracefully accept)
as, prima facie, the build logs remain functionally identical.

While here, whack default optimizations since CFLAGS are respected.

Reported by: fluffy, pkg-fallout