DTrace fixes for node.js

[Fedor Indutny]

Hello devs!

I have made some fixes to fix DTrace support for node.js in FreeBSD:

* http://www.freebsd.org/cgi/query-pr.cgi?pr=186821
* http://www.freebsd.org/cgi/query-pr.cgi?pr=187027

Here is a blog post with a bit of explanation of why this is needed
and what is fixed: https://blog.indutny.com/7.freebsd-dtrace

Please let me know if I could be any help in reviewing it.

Cheers,
Fedor.