Fix PRIdS define for Windows MINGW64

This merge requests fixes the PRIdS define being Iu instead of zu when targeting 64-bit Windows (MINGW64=1 as a compile flag), which caused game compilation to error out instead of building an executable.

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Note that I haven't tested 32-bit compiling as I don't have a working 32-bit compile setup, nor have I tested non-Windows compiling, but at least the latter should be fine.
For good measure, please test 32-bit Windows compiling before merging this.