use BB_EXECVP_or_die where appropriate

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

selinux/runcon.c

@@ -132,6 +132,5 @@ int runcon_main(int argc UNUSED_PARAM, char **argv)
 		bb_error_msg_and_die("can't set up security context '%s'",
 				     context_str(con));
 
-	execvp(argv[0], argv);
-	bb_perror_msg_and_die("can't execute '%s'", argv[0]);
+	BB_EXECVP_or_die(argv);
 }