X86: Implement VarHandle.compareAndExchange

Test: ART_HEAP_POISONING=true art/test.py --host -r -t 712-varhandle-invocation --32
Test: ART_HEAP_POISONING=false art/test.py --host -r -t 712-varhandle-invocation --32
Test: ART_USE_READ_BARRIER=true art/test.py --host -r -t 712-varhandle-invocation --32
Test: ART_USE_READ_BARRIER=false art/test.py --host -r -t 712-varhandle-invocation --32
Bug: 65872996
Change-Id: I880ba6176050591e7398f95b92fc3f74f566b042
2 files changed