JIT x64 codegen

[dobrakmato]

lets try to write simple JIT codegen for x64

• https://github.com/spencertipping/jit-tutorial
• http://ref.x86asm.net/coder64.html#
• http://www.c-jump.com/CIS77/CPU/x86/X77_0060_mod_reg_r_m_byte.htm
• https://nullprogram.com/blog/2015/03/19/

[dobrakmato]

Implemented in 6c81708.