Add x86-64 support to the PyPy JIT

by Jason Creighton for Python Software Foundation

The PyPy JIT, which has shown substantial performance improvements over other implementations of Python, including CPython and Unladen Swallow, does not currently support the x86-64 instruction set, making it impractical to use on 64-bit x86 systems. My proposal is to extend the existing x86 JIT backend to support x86-64 as well.