lua vs luajit vs both

[john at keeping.me.uk (John Keeping)]

On Tue, Jan 14, 2014 at 02:02:40AM +0100, Jason A. Donenfeld wrote:
> I've gone ahead and merged the lua work to master, for testing and
> subsequent cleanup before release.
> 
> Regarding "to jit or not to jit", I currently have this fancy autodetection
> logic:
> http://git.zx2c4.com/cgit/commit/?id=3488d124052f5c3ddef303ed5306ad6a458794c1
> 
> John -- I'm waiting for your input on the parent email, as you seem to be
> the originator of the opinion that "both are good".

It was more of a "there doesn't seem much overhead to supporting both,
since the API is the same".  I think the Makefile should take an
approach more like this though:

	ifdef NO_LUA
		CGIT_CFLAGS += -DNO_LUA
	else if defined(USE_LUAJIT)
		# LuaJIT code goes here
	else
		# Lua code goes here
	endif

Basically, use vanilla Lua by default by provide an easy way for users
to switch to LuaJIT if they want.