lua: Update to 5.4.4

Merge commit '755d9301ca89f02956fd17858b9d4d821ab5c972' from the
vendor branch. This updates us from lua 5.4.2 to 5.4.4.

In addition, it switches around how we flavor liblua for the boot loader
and flua. This is done to reduce diffs with upstream and make it easier
to import new versions (the current method has too many conflicts to
resolve by hand): we include luaconf.local.h from luaconf.h (the only
change to this file is now that #include at the end). We then define
what we need to: for flua (which does very little) and one for stand
(which creates the new FLOAT type out of int64).

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