FreeBSD support of build infrastructure

This adds FreeBSD support to osquery's build system, and only does it.  It could be the preliminary work of porting osquery to FreeBSD, and enables more people start to work on it without solving tedious build issues.

Build process:

1) Install dependencies:

autoconf
automake
bison
boost
cmake
gflags
git
glog
gmake
libtool
libunwind
rocksdb
snappy
thrift
thrift-cpp

tools/provision.sh did not install build packages for FreeBSD, just skips them.

2)
For now, the implementations of following tables do not exist (yet):

osquery/tables/specs/x/groups.table
osquery/tables/specs/x/passwd_changes.table
osquery/tables/specs/x/process_envs.table
osquery/tables/specs/x/process_open_files.table
osquery/tables/specs/x/processes.table
osquery/tables/specs/x/routes.table
osquery/tables/specs/x/users.table

By removing them temporarily, osquery can be built under FreeBSD with just `gmake`.
Ideally, we'd like to get to offer a 100% static build download as a forensics tool. Think of a drop-in "standalone" osquery with as small as footprint as possible. We statically compile/link as much as possible based on what's offered in the distro's package manager as a cheat for now.