-Wcstring-format-directive breaks existing code

[jakebromberg]

I have a custom logging function, defined as follows:
FOUNDATION_EXPORT void MyLogger(NSString *format, ...) NS_FORMAT_FUNCTION(1, 2);

When I call the function like so MyLogger(@"Error: stuff, %s", __PRETTY_FUNCTION__) I get following the clang diagnostic:
Using %s directive in CFString which is being passed as a formatting argument to the formatting CFfunction
This seems related to this change

The warning does not seem valid, since the type of the argument is known at compile time, even though the parameter is a va_list.