Octal literals in `case`s not supported?

```
$ cat main.c
int main(void) {
  int out = 0;
  switch (out) {
  case '\177':
    break;
  }
  return out;
}
$ gcc -std=c11 -pedantic main.c
$ ableC main.c
Error at line 4, column 7 in file main.c
         (parser state: 302; real character index: 240):
  Expected a token of one of the following types:
[...]
```