Need debug and release Skia builds

[mikerreed]

When we build skia(lib) as a dependency (which we do all over the place) we need to support passing in 'debug' or 'release', so the skialib will 'match' the setting in our tool/app.

This is important not just for performance (release is faster), but occasionally for correctness too ... A header might declare an object differently in those two modes, and if we're not consistent, we could break the ABI at runtime.

[luigi-rosso]

I'm totally guilty of not respecting this. I think I have all the configs set to build Skia in Release