I don't think build systems add -fPIC automatically, nor remove it automatically. C++ build systems do not stoop to the question of how to best build a C++ program, by and large. They are more task graph executors - either bad ones, like make, or good ones, like Bazel, but mostly task graph executors; the most "C++ support" you will get is native support for scanning #include files (as opposed to doing it yourself like make forces you to.)
I don't think build systems add -fPIC automatically, nor remove it automatically. C++ build systems do not stoop to the question of how to best build a C++ program, by and large. They are more task graph executors - either bad ones, like make, or good ones, like Bazel, but mostly task graph executors; the most "C++ support" you will get is native support for scanning #include files (as opposed to doing it yourself like make forces you to.)