A code review of barrier implementations for x86, ppc, aarch64, riscv reveals that none of the implementations of cmpxchg_oop() marks the overwritten remembered set card as dirty. We need to add code to dirty the remembered set card when in generational mode.

The code generated by cmpxchg_oop() needs to also include code generated by store_check(), which updates the remembered set only if mode is generational.