BSDmakefile passed --openssldir=etc. A relative openssldir is taken
relative to the prefix, so the generated files described /usr/etc.
FreeBSD has always used /etc/ssl (OPENSSLDIR in
secure/lib/libcrypto/Makefile.common), so configure with that.
Regenerate tools/c_rehash, the only committed generated file that
depends on openssldir. It is not installed. No compiled code changes.