[cmdline] Store exit status of failed command in errno

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/exec.c

 int execv ( const char *command, char * const argv[] ) {
 	struct command *cmd;
 	int argc;
+	int rc;
 
 	/* Count number of arguments */
 	for ( argc = 0 ; argv[argc] ; argc++ ) {}
 
 	/* An empty command is deemed to do nothing, successfully */
-	if ( command == NULL )
-		return 0;
+	if ( command == NULL ) {
+		rc = 0;
+		goto done;
+	}
 
 	/* Sanity checks */
 	if ( argc == 0 ) {
 		DBG ( "%s: empty argument list\n", command );
-		return -EINVAL;
+		rc = -EINVAL;
+		goto done;
 	}
 
 	/* Reset getopt() library ready for use by the command.  This
 
 	/* Hand off to command implementation */
 	for_each_table_entry ( cmd, COMMANDS ) {
-		if ( strcmp ( command, cmd->name ) == 0 )
-			return cmd->exec ( argc, ( char ** ) argv );
+		if ( strcmp ( command, cmd->name ) == 0 ) {
+			rc = cmd->exec ( argc, ( char ** ) argv );
+			goto done;
+		}
 	}
 
 	printf ( "%s: command not found\n", command );
-	return -ENOEXEC;
+	rc = -ENOEXEC;
+
+ done:
+	/* Store error number, if an error occurred */
+	if ( rc ) {
+		errno = rc;
+		if ( errno < 0 )
+			errno = -errno;
+	}
+
+	return rc;
 }
 
 /**