another infinite recursion

I think the fix to #301 didn't address what the user posted. It had self in the args.

I also hit the same issue myself and it was tough to debug.

failing test case:
https://github.com/gtrak/thiserror/commit/8c86fdfeb8fa36a99db41e54d128ee966e4b0b50#diff-52497d2243f5bec77c5ad6dc288f06f636be715b31c620c8ffc3ccaba340bacf

stderr:
```
┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈
error[E0425]: cannot find value `__FAIL__` in this scope
--> tests/ui/unconditional-recursion-2.rs:8:5
|
8 | __FAIL__;
| ^^^^^^^^ not found in this scope
┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈
```