Do not build pxeboot on i386/amd64.
When the pxeboot is too large, or unneeded, it may be disabled with this option.
See
.Va WITH_LOADER_PXEBOOT
for how to adjust the defaults when you need both a larger
.Pa /boot/loader
and
.Pa /boot/pxeboot
.Pp
This option only has an effect on x86.
