create an assembly label, and SYSCALLNUM to convert a syscall name into
the macro that's defined to be its number. Add a CALLSYS_NOERROR macro
which invokes the named system call. (CALLSYS_NOERROR is here since
it's used in locore, for sigcode.)
Support for AXPpci CPUs,
Support for AlphaStation 600 CPUs,
new boot block structure, which requires an 'installboot'
program and works a lot like the NetBSD/sparc boot blocks.