[C++] Remove explicit setting of O0 for debug mode.
[C++] Remove explicit setting of O0 for debug mode.

This flag is added automatically by CMake in Debug mode.

mikeb01/Aeron,EvilMcJerkface/Aeron,real-logic/Aeron,mikeb01/Aeron,EvilMcJerkface/Aeron,galderz/Aeron,galderz/Aeron,galderz/Aeron,mikeb01/Aeron,EvilMcJerkface/Aeron,real-logic/Aeron,mikeb01/Aeron,EvilMcJerkface/Aeron,real-logic/Aeron,real-logic/Aeron,galderz/Aeron