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/literals.lua

@@ -10,6 +10,7 @@ local function dostring (x) return assert(load(x), "")() end
 
 dostring("x \v\f = \t\r 'a\0a' \v\f\f")
 assert(x == 'a\0a' and string.len(x) == 3)
+_G.x = nil
 
 -- escape sequences
 assert('\n\"\'\\' == [[
@@ -129,16 +130,16 @@ end
 
 -- long variable names
 
-var1 = string.rep('a', 15000) .. '1'
-var2 = string.rep('a', 15000) .. '2'
-prog = string.format([[
+local var1 = string.rep('a', 15000) .. '1'
+local var2 = string.rep('a', 15000) .. '2'
+local prog = string.format([[
   %s = 5
   %s = %s + 1
   return function () return %s - %s end
 ]], var1, var2, var1, var1, var2)
 local f = dostring(prog)
 assert(_G[var1] == 5 and _G[var2] == 6 and f() == -1)
-var1, var2, f = nil
+_G[var1], _G[var2] = nil
 print('+')
 
 -- escapes --
@@ -150,13 +151,13 @@ assert([[
  $debug]] == "\n $debug")
 assert([[ [ ]] ~= [[ ] ]])
 -- long strings --
-b = "001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789"
+local b = "001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789"
 assert(string.len(b) == 960)
 prog = [=[
 print('+')
 
-a1 = [["this is a 'string' with several 'quotes'"]]
-a2 = "'quotes'"
+local a1 = [["this is a 'string' with several 'quotes'"]]
+local a2 = "'quotes'"
 
 assert(string.find(a1, a2) == 34)
 print('+')
@@ -164,12 +165,13 @@ print('+')
 a1 = [==[temp = [[an arbitrary value]]; ]==]
 assert(load(a1))()
 assert(temp == 'an arbitrary value')
+_G.temp = nil
 -- long strings --
-b = "001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789"
+local b = "001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789001234567890123456789012345678901234567891234567890123456789012345678901234567890012345678901234567890123456789012345678912345678901234567890123456789012345678900123456789012345678901234567890123456789123456789012345678901234567890123456789"
 assert(string.len(b) == 960)
 print('+')
 
-a = [[00123456789012345678901234567890123456789123456789012345678901234567890123456789
+local a = [[00123456789012345678901234567890123456789123456789012345678901234567890123456789
 00123456789012345678901234567890123456789123456789012345678901234567890123456789
 00123456789012345678901234567890123456789123456789012345678901234567890123456789
 00123456789012345678901234567890123456789123456789012345678901234567890123456789
@@ -199,19 +201,41 @@ x = 1
 ]=]
 
 print('+')
-x = nil
+_G.x = nil
 dostring(prog)
 assert(x)
+_G.x = nil
 
-prog = nil
-a = nil
-b = nil
+
+
+do  -- reuse of long strings
+
+  -- get the address of a string
+  local function getadd (s) return string.format("%p", s) end
+
+  local s1 <const> = "01234567890123456789012345678901234567890123456789"
+  local s2 <const> = "01234567890123456789012345678901234567890123456789"
+  local s3 = "01234567890123456789012345678901234567890123456789"
+  local function foo() return s1 end
+  local function foo1() return s3 end
+  local function foo2()
+    return "01234567890123456789012345678901234567890123456789"
+  end
+  local a1 = getadd(s1)
+  assert(a1 == getadd(s2))
+  assert(a1 == getadd(foo()))
+  assert(a1 == getadd(foo1()))
+  assert(a1 == getadd(foo2()))
+
+  local sd = "0123456789" .. "0123456789012345678901234567890123456789"
+  assert(sd == s1 and getadd(sd) ~= a1)
+end
 
 
 -- testing line ends
 prog = [[
-a = 1        -- a comment
-b = 2
+local a = 1        -- a comment
+local b = 2
 
 
 x = [=[
@@ -228,10 +252,11 @@ for _, n in pairs{"\n", "\r", "\n\r", "\r\n"} do
   assert(dostring(prog) == nn)
   assert(_G.x == "hi\n" and _G.y == "\nhello\r\n\n")
 end
+_G.x, _G.y = nil
 
 
 -- testing comments and strings with long brackets
-a = [==[]=]==]
+local a = [==[]=]==]
 assert(a == "]=")
 
 a = [==[[===[[=[]]=][====[]]===]===]==]