Fix #259: Move *software-version* from LISP to SYSTEM package
For simplicity, just export *software-version*
from the system
package, like *software-type*
. This fixes the compiler warning
about lisp::*software-version*
being undefined when compiling
linux-os.lisp.
Use boot-2023-08.lisp to bootstrap this change because we need to
unintern lisp::*software-version*
.