Clashing Options in Apple Bitcode Bundle on macOS

Hi wonderful Bazel folks,

I'd noticed that if you try to build a macos_bundle with bitcode enabled (--apple_bitcode=embedded), the options clash with the following error: `ld: -bundle and -bitcode_bundle (Xcode setting ENABLE_BITCODE=YES) cannot be used together`

Looks like the -bundle option is set in [AppleBinary.java](https://github.com/bazelbuild/bazel/blob/master/src/main/java/com/google/devtools/build/lib/rules/objc/AppleBinary.java). Perhaps a good fix would be to not just set the option if --apple_bitcode is also enabled?

Thanks so much,
Chris