gdb: sim: add command line completion

For now, only the sub-command name is completed.  No support yet for
completing options to that command.  But even this is a huge step as
currently, nothing is completed, and the basic "help sim" is fairly
obtuse as to what exactly the "sim" command accepts.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

include/gdb/remote-sim.h

@@ -276,6 +276,10 @@ void sim_stop_reason (SIM_DESC sd, enum sim_stop *reason, int *sigrc);
 
 void sim_do_command (SIM_DESC sd, char *cmd);
 
+/* Complete a command based on the available sim commands.  Returns an
+   array of possible matches.  */
+char **sim_complete_command (SIM_DESC sd, char *text, char *word);
+
 #ifdef __cplusplus
 }
 #endif