Build Configuration and --compilation_mode

Is XCHammer intended to pass a `-c`/`--compilation_mode` flag based on Xcode's build configuration?

In Xcode, the app target has "Debug" as its build configuration, but this appears to not be reflected in the `bazel build` invocation. I had to add `-c dbg` to the config in order to get a debug build.

I'm not sure how relevant this is, but [Tulsi's has a doc](https://github.com/bazelbuild/tulsi/blob/e51d9b4b1572084e6cbd960da96d451c17f0e60f/site/docs/gettingstarted.md#what-bazel-flags-are-used-when-building) that says it sets `--compilation_mode` based on Xcode.

However, I don't see either `-c` or `--compilation_mode` string in `build_bazel.py`.