GStatBuf is not usable on 32 bit Windows without the redefinition in
pbd/gstdio_compat.h so add a test to check for the correct behavior of
g_stat and g_utime on all platforms now that the issue is fixed.
From this I can see that PBD::copy_file is not working correctly on windows
as it is adding windows style line endings. Adding O_BINARY to ::open flags
would fix it, but perhaps there is a better way...