Make all the supported 3rd party libraries working on iOS platform

Now the script in `build/ios/` support building the following 3rd party libraries:

- png
- zlib
- lua
- luajit
- websockets
- curl
- freetype2
- jpeg
- tiff
- webp

All the above libraries are tested on my own computer.
Note: it is working only for iOS now, other platform will be added later.