build.sh: Terser output, more success running lipo

Use xcrun to run the right version of lipo. This requires doing different
architectures for each SDK.

Log xcodebuild runs, then report on their success or failure. This is made
optional with the new "-v" flag.
add (untested) support for controlling GL blend equations.

GL_MIN and GL_MAX are omitted because they are absent in iOS; rumor
has it they may exist under the names "GL_MIN_EXT" and "GL_MAX_EXT",
but this seemed harder to accomplish.

The intent is that if you don't use setBlendEquation(), you'll never
see any changes, but it's there as an alternative if you have reason
to prefer subtractive rendering.
Merge pull request #644 from seebs/seebs

GL blend functions, build.sh tweaks