Improvements to OSS Test CMake generation and add tests (#3649)

Summary:
* Fix the bash script looping through exectubales
* For the generator, add a way to add additional libs in generated CMakeLists.txt
* Build extension/data_loader in main target as an example for the fix

Pull Request resolved: https://github.com/pytorch/executorch/pull/3649

Test Plan: `sh test/run_oss_cpp_tests.sh`

Reviewed By: larryliu0820

Differential Revision: D57467885

Pulled By: kirklandsign

fbshipit-source-id: 49f9b8dac9f091aca05a122aaf0cb9020d192b68