CMake Error Some (but not all) targets in this export set were already defined.

## Problems when install polymetis from source code

## Description
When l follow the tutorial in [this](https://facebookresearch.github.io/fairo/polymetis/installation.html) and try to install from source. l follow the oreder and 1 ,2 ,3 is ok. In the 4th step, l run
~~~
cmake .. -DCMAKE_BUILD_TYPE=Release -DBUILD_FRANKA=ON -DBUILD_TESTS=ON -DBUILD_DOCS=ON
~~~
and l got this
By the way, l install grpc and protobuf before the cmake. And l run the grpc helloworld demo. So l guess l install grpc and protobuf successfully.

## HELP!!!!
Anyone can help me, l really unfamilar with cmake or make these things.l'd appreciate that anyone can offer any useful infos.

Start with the source-installation tutorial and reproduce the fourth-step CMake command with BUILD_FRANKA, BUILD_TESTS, and BUILD_DOCS enabled. Capture the complete configure output and inspect the CMake export definitions involved in the already-defined targets error. Done means the configuration completes without the export-set conflict.

Written by the indexing model from the issue text.