Since we always include the raw syscall number when tracing, also
including it in the name when it's unknown is redundant. Simplify
the code by using a constant string.
Many ports have the same sim syscall logic, so add some helpers to handle
all the common details. The arches still have to deal with the unpacking
and packing of the syscall arguments, but the rest of the sim<->callback
glue is now shared.
Joel Brobecker
Mike Frysinger