It causes a build error with MinGW:
CC gsf-input.lo
gsf-input.c:632:1: error: conflicting types for 'gsf_input_set_modtime_from_stat'
gsf_input_set_modtime_from_stat (GsfInput *input,
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ../gsf/gsf.h:54:0,
from gsf-input.c:24:
../gsf/gsf-input-impl.h:67:10: note: previous declaration of 'gsf_input_set_modtime_from_stat' was here
gboolean gsf_input_set_modtime_from_stat (GsfInput *input,
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Makefile:705: recipe for target 'gsf-input.lo' failed
<sys/stat.h>
is enough portable because glib/gstdio.h uses it.