[clang] [clang] Update -Wformat warnings for fixed-point format specifiers (PR #82855)

[via cfe-commits]

PiJoules wrote:

> > Do you know a libc implementation that actually implements `%k` `%r` and who are the potential users? From a quick glance, gcc avr supports fixed-point types but avr-libc doesn't seem to support %k %r.
> 
> LLVM-libc will support them soon, PR should be coming next week. We have internal customers at Google that are starting to use fixed-point types in their embedded products.

https://github.com/llvm/llvm-project/pull/82707 is the libc PR

https://github.com/llvm/llvm-project/pull/82855