Fixed files to support FreeBSD amd64 based on patches at:

Fixed files to support FreeBSD amd64 based on patches at:
http://www.freebsd.org/cgi/cvsweb.cgi/ports/devel/glog/files/

Since FreeBSD do not have gettid system call unlikely to MacOSX, I
modified utilities.h not to use that on FreeBSD:
* FreeBSD lacks gettid syscall.
http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/kern/syscalls.master?rev=1.276;content-type=text%2Fplain
* MacOSX gettid == 286.
http://www.opensource.apple.com/source/xnu/xnu-1504.3.12/bsd/kern/syscalls.master

As for the fix of stacktrace, we use a different approach.
Even in FreeBSD, package gcc44/gcc46 has unwind.h.
As a result, checking unwind.h should be natural solution.

This patch was given by yyanagisawa

git-svn-id: https://google-glog.googlecode.com/svn/trunk@116 eb4d4688-79bd-11dd-afb4-1d65580434c0