[libc++abi] Remove the LIBCXXABI_ENABLE_PIC option

Instead, people should be using CMAKE_POSITION_INDEPENDENT_CODE to control
whether they want to use PIC or not. We should try to avoid reinventing
the wheel whenever CMake natively supports something.

This makes libc++abi consistent with libc++ and libunwind.

Differential Revision: https://reviews.llvm.org/D103973

GitOrigin-RevId: a0ae3b0789140ee9238c3052b2231ceaa777e82f
2 files changed