[build] Add the depfile as an output for gen_kernel_bytecode_dill
[build] Add the depfile as an output for gen_kernel_bytecode_dill

This will ensure that the depfile's directory is created before running
gen_kernel.

Change-Id: I82452b0161e533f31e1749f8e5894be7e58a6b4d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/139146
Reviewed-by: Siva Annamalai <2e618a8cbd7bb6b3d4409061ae407d692a098546@google.com>
Commit-Queue: Jason Simmons <345008440c885d4763d50f58e545b9839f60f79f@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk