Port my AOSP QuasiAtomic rewrite to art.

Change-Id: I9e8fe487b15083cfc441a90ec1ec0eb5e645229e
diff --git a/src/native/sun_misc_Unsafe.cc b/src/native/sun_misc_Unsafe.cc
index 214771b..8cc549a 100644
--- a/src/native/sun_misc_Unsafe.cc
+++ b/src/native/sun_misc_Unsafe.cc
@@ -54,7 +54,7 @@
   byte* raw_addr = reinterpret_cast<byte*>(obj) + offset;
   volatile int64_t* address = reinterpret_cast<volatile int64_t*>(raw_addr);
   // Note: android_atomic_cmpxchg() returns 0 on success, not failure.
-  int result = QuasiAtomicCas64(expectedValue, newValue, address);
+  int result = QuasiAtomic::Cas64(expectedValue, newValue, address);
   return (result == 0);
 }