Make fixes and improvements

- Polyfill UTIME_OMIT on XNU
- Refactor Lua build code so it's better
- Add unix module to lua.com (Discord request)
- Add unix.utimensat() and unix.futimens() to redbean
- Avoid creating double slash path in linenoise (#428)
- Remove double slashes in NT paths automatically (#428)
- Make strerror() smarter about showing NT errors (#428)

Fixes #428

tool/net/lfuncs.h

@@ -7,7 +7,6 @@ COSMOPOLITAN_C_START_
 
 int LuaMaxmind(lua_State *);
 int LuaRe(lua_State *);
-int LuaUnix(lua_State *);
 int luaopen_argon2(lua_State *);
 int luaopen_lsqlite3(lua_State *);