Adding FLAVORS to lua-luarocks

[Russell Haley]

Hello,

I have a review for updating the Lua package manager - LuaRocks - it to the
latest revision, 3.2.1. The new port file uses an update to lua.mk from
Andrew Gierth for using FLAVORS to support all available versions of Lua.
The reviews are here:  (LuaRocks) https://reviews.freebsd.org/D17814 and
here: (Lua.mk) https://reviews.freebsd.org/D16494

In the LuaRocks port, I've added the flavors as a selection of port OPTIONS
to build the correct version. Unfortunately, using the OPTIONS isn't ideal
because it will save the selected option for the next time the port is run,
but that's not the desired use case. I wanted the build to *always* prompt
for a Lua version so it can be used for multiple side by side Lua
installations.

Any suggestions, alternatives to OPTIONS or other constructive input would
be appreciated.

Cheers,
Russ