[PowerPC] Add option to control PCRel GOT indirect linker optimization

Add a hidden option to the compiler to control a the PC Relative GOT indirect
linker optimization.

If this option is set to false the compiler will no loger produce the
relocations required by the linker to perform the optimization.

Reviewed By: nemanjai, NeHuang, #powerpc

Differential Revision: https://reviews.llvm.org/D85377