Don't use -N to set the OMAGIC with data and text writeable and data
not page aligned. To do this, use the ld script gnu ld installs on my
system.

This is imperfect: LDFLAGS_BIN and LD_FLAGS_BIN describe different
things. The loader script could be better named and take into account
other architectures. And having two different mechanisms to do
basically the same thing needs study. However, it's blocking forward
progress on lld, so I'll work in parallel to sort these out.

Differential Revision: https://reviews.freebsd.org/D7409
Reviewed by: emaste