Port from 5.0: Fix relro, now, and PIE for Libraries (#43036)
Port from 5.0: Fix relro, now, and PIE for Libraries (#43036)

* Runtime PR685 Port: Fix relro, now, and PIE for libraries.

* Fixed a policy and PIE settings in Unix Native libraries.

* Backed out add_link_options since it's not supported in this repo's version of CMake.

* Fixed a wrong indentation.

* Added missing CMAKE_SHARED_LINKER_FLAGS clause.
BrennanConroy/corefx,BrennanConroy/corefx,BrennanConroy/corefx