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

Builds under Cygwin and Linux with these changes
C99 `inttypes.h` already provides what we need, but I think it's not available on MSVC.

Maybe we can just include that header on all platforms but MSVC and define what we need for MSVC, something like:

```
+#   if (!defined (PRId64))
+#       define PRId64   %I64d
+#   endif
```

`glib.h` seems like a sensible place to plug this in to me.