Fixing warnings in utils/metadata when building under Windows/Cygwin

Builds under Cygwin and Linux with these changes
At least `stdint.h` is included since VS 2010, but I'm not sure about `inttypes.h`.

Honestly I'm not sure if it'd be worth, I'd just deal with the defines explicitly for the MSVC case, but if it works I don't see any objection to using it.