[patch]: Fix bootstrap/PR 25502: I64d format Werror problem in build

[Aaron W. LaFramboise]

Joseph S. Myers wrote:

> The C front-end change is OK, but the rest will need MinGW maintainer 
> review and the MinGW maintainers will need to judge its suitability for 
> Stage 3.

I recommend Danny approve this for stage 3 because this is one of the 
last things preventing --enable-werror builds from working, which is a 
valuable feature.  It's also a bug, PR25502.