Upgrade Lua to 5.4.3 (#217)

Based on https://github.com/lua/lua/releases/tag/v5.4.3 (commit eadd8c7).

third_party/lua/test/tracegc.lua

@@ -0,0 +1,40 @@
+-- track collections
+
+local M = {}
+
+-- import list
+local setmetatable, stderr, collectgarbage =
+         setmetatable, io.stderr, collectgarbage
+
+_ENV = nil
+
+local active = false
+
+
+-- each time a table is collected, remark it for finalization on next
+-- cycle
+local mt = {}
+function mt.__gc (o)
+  stderr:write'.'    -- mark progress
+  if active then
+    setmetatable(o, mt)   -- remark object for finalization
+  end
+end
+
+
+function M.start ()
+  if not active then
+    active = true
+    setmetatable({}, mt)    -- create initial object
+  end
+end
+
+
+function M.stop ()
+  if active then
+    active = false
+    collectgarbage()   -- call finalizer for the last time
+  end
+end
+
+return M