Bring Lua to 5.4.6. (#1214)

This essentially re-does the work of #875 on top of master.

This is what I did to check that Cosmo's Lua extensions still worked:

```
$ build/bootstrap/make MODE=aarch64 o/aarch64/third_party/lua/lua
$ ape o/aarch64/third_party/lua/lua
>: 10
10
>: 010
8
>: 0b10
2
>: string.byte("\e")
27
>: "Hello, %s" % {"world"}
Hello, world
>: "*" * 3
***
```

`luaL_traceback2` was used to show the stack trace with parameter
values; it's used in `LuaCallWithTrace`, which is used in Redbean to run
Lua code. You should be able to see the extended stack trace by running
something like this: `redbean -e "function a(b)c()end a(2)"` (with
"params" indicating the extended stack trace):

```
stack traceback:
 [string "function a(b)c()end a(2)"]:1: in function 'a', params: b = 2;
 [string "function a(b)c()end a(2)"]:1: in main chunk
```
@pkulchenko confirmed that I get the expected result with the updated
code.

This is what I did to check that Lua itself still worked:

```
$ cd third_party/lua/test/
$ ape ../../../o/aarch64/third_party/lua/lua all.lua
```

There's one test failure, in `files.lua`:

```
***** FILE 'files.lua'*****
testing i/o
../../../o/aarch64/third_party/lua/lua: files.lua:84: assertion failed!
stack traceback:
[C]: in function 'assert'
files.lua:84: in main chunk
(...tail calls...)
all.lua:195: in main chunk
[C]: in ?
.>>> closing state <<<
```

That isn't a result of these changes; the same test is failing in
master.

The failure is here:

```lua
if not _port then   -- invalid seek
  local status, msg, code = io.stdin:seek("set", 1000)
  assert(not status and type(msg) == "string" and type(code) == "number")
end
```

The test expects a seek to offset 1,000 on stdin to fail — but it
doesn't. `status` ends up being the new offset rather than `nil`.

If I comment out that one test, the remaining tests succeed.

third_party/lua/test/pm.lua

@@ -9,12 +9,12 @@ local function checkerror (msg, f, ...)
 end
 
 
-function f(s, p)
+local function f (s, p)
   local i,e = string.find(s, p)
   if i then return string.sub(s, i, e) end
 end
 
-a,b = string.find('', '')    -- empty patterns are tricky
+local a,b = string.find('', '')    -- empty patterns are tricky
 assert(a == 1 and b == 0);
 a,b = string.find('alo', '')
 assert(a == 1 and b == 0)
@@ -88,7 +88,7 @@ assert(f("alo alo", "%C+") == "alo alo")
 print('+')
 
 
-function f1(s, p)
+local function f1 (s, p)
   p = string.gsub(p, "%%([0-9])", function (s)
         return "%" .. (tonumber(s)+1)
        end)
@@ -113,7 +113,7 @@ local abc = string.char(range(0, 127)) .. string.char(range(128, 255));
 
 assert(string.len(abc) == 256)
 
-function strset (p)
+local function strset (p)
   local res = {s=''}
   string.gsub(abc, p, function (c) res.s = res.s .. c end)
   return res.s
@@ -147,7 +147,7 @@ assert(string.gsub('
 assert(string.gsub('alo úlo  ', ' +$', '') == 'alo úlo')  -- trim
 assert(string.gsub('  alo alo  ', '^%s*(.-)%s*$', '%1') == 'alo alo')  -- double trim
 assert(string.gsub('alo  alo  \n 123\n ', '%s+', ' ') == 'alo alo 123 ')
-t = "abç d"
+local t = "abç d"
 a, b = string.gsub(t, '(.)', '%1@')
 assert('@'..a == string.gsub(t, '', '@') and b == 5)
 a, b = string.gsub('abçd', '(.)', '%0@', 2)
@@ -184,6 +184,7 @@ do
   local function setglobal (n,v) rawset(_G, n, v) end
   string.gsub("a=roberto,roberto=a", "(%w+)=(%w%w*)", setglobal)
   assert(_G.a=="roberto" and _G.roberto=="a")
+  _G.a = nil; _G.roberto = nil
 end
 
 function f(a,b) return string.gsub(a,'.',b) end
@@ -195,20 +196,21 @@ assert(string.gsub("alo $a='x'$ novamente $return a$",
                    "$([^$]*)%$",
                    dostring) == "alo  novamente x")
 
-x = string.gsub("$x=string.gsub('alo', '.', string.upper)$ assim vai para $return x$",
+local x = string.gsub("$x=string.gsub('alo', '.', string.upper)$ assim vai para $return x$",
          "$([^$]*)%$", dostring)
 assert(x == ' assim vai para ALO')
+_G.a, _G.x = nil
 
-t = {}
-s = 'a alo jose  joao'
-r = string.gsub(s, '()(%w+)()', function (a,w,b)
-      assert(string.len(w) == b-a);
-      t[a] = b-a;
-    end)
+local t = {}
+local s = 'a alo jose  joao'
+local r = string.gsub(s, '()(%w+)()', function (a,w,b)
+             assert(string.len(w) == b-a);
+             t[a] = b-a;
+           end)
 assert(s == r and t[1] == 1 and t[3] == 3 and t[7] == 4 and t[13] == 4)
 
 
-function isbalanced (s)
+local function isbalanced (s)
   return not string.find(string.gsub(s, "%b()", ""), "[()]")
 end
 
@@ -251,7 +253,7 @@ if not _soft then
 end
 
 -- recursive nest of gsubs
-function rev (s)
+local function rev (s)
   return string.gsub(s, "(.)(.+)", function (c,s1) return rev(s1)..c end)
 end