glib-2.0: Use 'GStatBuf' as ctype for 'Stat'

glib-2.0: Use 'GStatBuf' as ctype for 'Stat'

The documentation of g_stat () states:

In Microsoft's compiler, by default struct stat means one with
64-bit time fields while in MinGW struct stat is the legacy one
with 32-bit fields.

To hopefully clear up this mess, the gstdio.h header defines a
type GStatBuf which is the appropriate struct type depending
on the platform and/or compiler being used. On POSIX it is just
struct stat, but note that even on POSIX platforms, stat() might
be a macro.