use g_ascii_iscntrl instead of c_iscntrl from gnulib
use g_ascii_iscntrl instead of c_iscntrl from gnulib

Signed-off-by: Pavel Hrdina <d4772d05997b8abf035041e3b4f4996380ea7e7a@redhat.com>
Reviewed-by: Cole Robinson <7cd45ff6ad1fb7cf556a02797d774247851499f8@redhat.com>

crobinso/libvirt,libvirt/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,libvirt/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,zippy2/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,olafhering/libvirt,nertpinx/libvirt,zippy2/libvirt,jfehlig/libvirt,libvirt/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,zippy2/libvirt,olafhering/libvirt,jardasgit/libvirt,crobinso/libvirt,jardasgit/libvirt,crobinso/libvirt,olafhering/libvirt,crobinso/libvirt,jfehlig/libvirt,zippy2/libvirt,nertpinx/libvirt,olafhering/libvirt,libvirt/libvirt,nertpinx/libvirt