OpenPOWER Firefox JIT update

As of this afternoon, the Baseline Interpreter-only form of the OpenPOWER JIT (64-bit little-endian) now passes all of the JIT tests except for the Wasm ones, which are being actively worked on. Remember, this is just the first of the three phases and we need all three for the full benefit, but it already yields a noticeable boost in my internal tests over the C++ interpreter. The MVP is Baseline Interpreter and Wasm, so once it passes the Wasm tests as well, it's time to pull it current with 91ESR. You can help.