cmake support

[Andarwinux]

ref:
LuaJIT/LuaJIT#476
https://github.com/WohlSoft/LuaJIT

Hi, luajit's current build system is very messy and upstream rejects pr for cmake support. is it possible to add cmake support to this branch? Here is a branch with cmake support.

[yhyu13]

@Andarwinux

There is a new project raised here https://github.com/tarantool/luajit which also forks luajit but has very complete cmake supports