Export C++ CMake target for external linking

[hmacdope]

Export a target with a cmake.config file such that an external CMake package can use FindPackage to discovery distopia

See:
https://github.com/fastfloat/fast_float/blob/main/CMakeLists.txt#L73C4-L76C54

and

https://github.com/google/highway/blob/master/CMakeLists.txt#L795C1-L796C1