Coerce Rational to Integer in X86_64 c compiler to allow usage of & operator.

I'm not entirely sure how to reproduce this in a minimal way, but sometimes the the expr `(localspc/8 + @state.dirty.length)` ends up being an instance of Rational (part of Ruby stdlib), which does not have the `&` operator defined. This works around the issue by forcing the Rational back to an Integer.

If you want the C source code I was using to trigger this error, send me an email (joev@metasploit.com) and I'll send it over to you.