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

[Michael Jones via cfe-commits]

michaelrj-google wrote:

This patch looks fine from my end, but I was wondering: Does clang do warnings for printf flags that don't apply to a specific conversion? As an example, in the format specifier `"%+R"` is technically undefined since the `+` flag only applies to signed  conversions. In practice it's not a big deal (we just ignore irrelevant flags) but it could be an area of further development.

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