Make sure our in-source include directories come first.
Make sure our in-source include directories come first.

This avoids including a header from a previously installed version of
cpp-driver.

hpcc-systems/cpp-driver,datastax/cpp-driver,datastax/cpp-driver,datastax/cpp-driver,hpcc-systems/cpp-driver,hpcc-systems/cpp-driver,mikefero/cpp-driver,hpcc-systems/cpp-driver,mikefero/cpp-driver,mikefero/cpp-driver,datastax/cpp-driver,mikefero/cpp-driver,mikefero/cpp-driver