[clang] [clang] Catch missing format attributes (PR #70024)

[Budimir Aranđelović via cfe-commits]

budimirarandjelovicsyrmia wrote:

Problem is in function f41 where diagnosing depends on architecture and operating system.
```
void f41(char *out, ... /* args */) // #f41
{
    va_list args;
    char *ch;
    vscanf("%s", ch);
    vprintf(out, args);
}
```

As this is unusual situation, I suppose to remove this function from test.

https://github.com/llvm/llvm-project/pull/70024