Atomics.wake(...) always returns 0 on non-win32 platforms

While working on Atomics tests for Test262, I observed that any test which checked that the return value of `Atomics.wake(...)` was some non-zero value, the test would fail. I've tracked the cause:

https://github.com/Microsoft/ChakraCore/blob/c0723f4985c468937c6ac12260bdbe5da6d25539/lib/Runtime/Library/SharedArrayBuffer.cpp#L764-L780