[Bug c/92857] -Wsign-conversion flag issues false positives for expression using typedef'ed unsigned types

[joshua.a.saxby at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92857

--- Comment #3 from Joshua Saxby <joshua.a.saxby at gmail dot com> ---
I can confirm that if `MyUnsigned` is changed to `unsigned char`, the issue
persists, however if it is changed to `unsigned int`, the issue is not present.