newvers.sh. Pass it in from include/Makefile. If it isn't passed in,
fall back to the old logic of using dirname $0.
Using dirname $0 does not yield the path to the script if it was
sourced in from another script in another directory; you end up with
the parent script's path. That was causing newvers.sh to look one
level below the FreeBSD src/ directory when building osreldate.h and it
may find something like a git or svn repo there that has nothing to do
with FreeBSD.
PR: 174422
Approved by: re ()
MFC after: 2 weeks
0210509acd