Move realpath.c to upstream-freebsd.

This is actually a slightly newer upstream version than the one I
originally pulled. Hopefully now it's in upstream-freebsd it will
be easier to track upstream, though I still need to sit down and
write the necessary scripts at some point.

Bug: 5110679
Change-Id: I87e563f0f95aa8e68b45578e2a8f448bbf827a33
6 files changed