GL blend functions, build.sh tweaks

The GL function stuff is untested but at least builds. Open issues:
* It'd be nice to support GL_MIN and GL_MAX, but apparently those are extensions and may not be available for iOS.
* I wanted to also support glBlendFuncSeparate and glBlendModeSeparate, but those, too, are apparently extensions and some Android devices won't support them.

The build.sh stuff fixes the lipo errors by only running it for each SDK against the architectures that SDK supports, and also makes the output a little more manageable.