The WinCE, a.out and FreeBSD loaders are designed to be #included by
core/loader.c, which no longer exists.  These old loaders are not
usable anymore and cause compilation failures when enabled in
config/general.h.

Signed-off-by: Marin Hannache <mareo@mareo.fr>
Signed-off-by: Michael Brown <mcb30@ipxe.org>