[tlbuild] lua52 and lua53

[Akira Kakuto]

Hi Norbert,

> it seems that we now have libs/lua52 and libs/lua53, and
> when enabling --enable-shared we get libtexlua52 and ...53,
> but texlua the program is
> only linked against libtexlua52.
>
> Is there a reason for having both of them?
> What is the plan here?

In TeX Live 2018, only luatex53 on lua-5.3 is provided for the
tests of lua-5.3 scripts: luatex53 --luaonly ...
texlua53 etc. are not provided. luatex53 is only for tests,
and will be removed in TeX Live 2019. We will have "luatex" on
lua-5.3 in TL 2019.
luatex53 is not used as a TeX engine in TL 2018.
Details will be given by Luigi or Hans.

Best,
Akira