[Bug c/92292] duplicate -Wformat warnings about incorrect printf format specifiers

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92292

--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
This would be an interaction between the built-in function having a printf 
format attribute and the header having either a gnu_printf or an ms_printf 
format attribute (depending on feature test macros); as those attributes 
aren't exact duplicates, both are applied (it's perfectly valid for a 
function to have multiple format attributes, but I suppose we should 
special-case this for format attributes for built-in functions with a more 
specific format attribute in the header declaration).