[Bug target/116063] [PPC] Transparent union issue with signedness when optimizing

[hstong at ca dot ibm.com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116063

--- Comment #2 from Hubert Tong <hstong at ca dot ibm.com> ---
If it is invalid, a diagnostic like this should appear:
```
warning: union cannot be made transparent
```