sim: namespace sim_machs

We want to do a single build with all arches in one binary which means
we need to namespace sim_machs on a per-arch basis.  Move it from a
global variable to the sim description structure so it can be setup at
runtime.

Changing the SIM_MODEL->num from an enum to an int is unfortunate, but
we specifically don't want to maintain a centralized list anymore, and
this was never used directly in common code, just passed to per-arch
callbacks.

sim/bpf/sim-if.c

@@ -111,6 +111,8 @@ bpf_free_state (SIM_DESC sd)
   sim_state_free (sd);
 }
 
+extern const SIM_MACH * const bpf_sim_machs[];
+
 /* Create an instance of the simulator.  */
 
 SIM_DESC
@@ -125,6 +127,9 @@ sim_open (SIM_OPEN_KIND kind,
 
   SIM_DESC sd = sim_state_alloc (kind, callback);
 
+  /* Set default options before parsing user options.  */
+  STATE_MACHS (sd) = bpf_sim_machs;
+
   if (sim_cpu_alloc_all (sd, 1) != SIM_RC_OK)
     goto error;