[vm] x86_64 registers
[vm] x86_64 registers

Backport
https://github.com/ocaml/ocaml/commit/bc333918980b97a2c81031ec33e72a417f854376
from OCaml VM

SkySkimmer/coq,gares/coq,coq/coq,Zimmi48/coq,silene/coq,coq/coq,SkySkimmer/coq,coq/coq,coq/coq,Zimmi48/coq,JasonGross/coq,JasonGross/coq,Matafou/coq,silene/coq,JasonGross/coq,Zimmi48/coq,ejgallego/coq,SkySkimmer/coq,gares/coq,ejgallego/coq,gares/coq,ejgallego/coq,Matafou/coq,Zimmi48/coq,JasonGross/coq,Matafou/coq,SkySkimmer/coq,gares/coq,ejgallego/coq,silene/coq,gares/coq