emulators/pcsx2: Fix SIGILL crash

Do not pass -march=native as that can bring pre-built packages with
instructions not supported by end users and lead to a SIGILL crash.

If CPUTYPE is not defined, set arch to the oldest CPU that supports
SSE 4.1 (penryn), else let the build system try to build with whatever
is set.

Add a message indicating that the port should be rebuilt with CPUTYPE
defined for best performance.

While here, use zstd from ports (now detected).

PR: 272192
Reported by: Patrick McMunn <doctorwhoguy@gmail.com>