objtool: Print top level commands on incorrect usage

Print top-level objtool commands, along with the error on incorrect
command line usage. Objtool command line parser exit's with code 129,
for incorrect usage. Convert the cmd_usage() exit code also, to maintain
consistency across objtool.

After the patch:

$ ./objtool -j

Unknown option: -j

usage: objtool COMMAND [ARGS]

Commands:
check Perform stack metadata validation on an object file
orc Generate in-place ORC unwind tables for an object file

$ echo $?
129

Signed-off-by: Kamalesh Babulal <[e-mail]>
Acked-by: Josh Poimboeuf <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

tools/objtool/objtool.c

···
 
 	printf("\n");
 
-	exit(1);
+	exit(129);
 }
 
 static void handle_options(int *argc, const char ***argv)
···
 			break;
 		} else {
 			fprintf(stderr, "Unknown option: %s\n", cmd);
-			fprintf(stderr, "\n Usage: %s\n",
-				objtool_usage_string);
-			exit(1);
+			cmd_usage();
 		}
 
 		(*argv)++;