CMake Option provided for building XRT components with static linkage, but user has no choice

[wilderfield]

CMake Option provided for building XRT components with static linkage, but user has no choice

https://github.com/Xilinx/XRT/blob/master/src/CMake/nativeLnx.cmake#L62-L73

The point of CMake options is to allow the person building your software to control how it is built... (what features do they want?). i.e.

cmake -DXRT_STATIC_BUILD=ON ..

In the referenced usage, control is taken away from the user, and if the system is Ubuntu... static targets are generated regardless of the users opinion.

We should try to improve upon this.