[C++]: Fix CMakeLists.txt to prevent duplicate addition of the driver source directories.
[C++]: Fix CMakeLists.txt to prevent duplicate addition of the driver source directories.

EvilMcJerkface/Aeron,tbrooks8/Aeron,oleksiyp/Aeron,real-logic/Aeron,gkamal/Aeron,oleksiyp/Aeron,tbrooks8/Aeron,tbrooks8/Aeron,real-logic/Aeron,EvilMcJerkface/Aeron,real-logic/Aeron,oleksiyp/Aeron,galderz/Aeron,mikeb01/Aeron,galderz/Aeron,mikeb01/Aeron,gkamal/Aeron,EvilMcJerkface/Aeron,real-logic/Aeron,mikeb01/Aeron,galderz/Aeron,mikeb01/Aeron,EvilMcJerkface/Aeron,galderz/Aeron,gkamal/Aeron