enaml recipe build fail

### Logs

```
[1m[INFO][0m: [36m-> directory context /home/bobf/ex/regression/.buildozer/android/platform/build-arm64-v8a/build/other_builds/atom/arm64-v8a__ndk_target_21/atom[39m
[1m[90m[DEBUG][39m[0m: [90m->[0m running python3 setup.py build_ext -v[0m
[1m[90m[DEBUG][39m[0m: Traceback (most recent call last):
[1m[90m[DEBUG][39m[0m: File "/home/bobf/ex/regression/.buildozer/android/platform/build-arm64-v8a/build/other_builds/atom/arm64-v8a__ndk_target_21/atom/setup.py", line 13, in
[1m[90m[DEBUG][39m[0m: from cppy import CppyBuildExt
[1m[90m[DEBUG][39m[0m: ImportError: cannot import name 'CppyBuildExt' from 'cppy' (/home/bobf/ex/regression/.buildozer/android/platform/build-arm64-v8a/build/other_builds/hostpython3/desktop/hostpython3/native-build/Lib/site-packages/cppy/__init__.py)
[1m[90m[DEBUG][39m[0m:
[1m[90m[DEBUG][39m[0m: The above exception was the direct cause of the following exception:
[1m[90m[DEBUG][39m[0m:
[1m[90m[DEBUG][39m[0m: Traceback (most recent call last):
[1m[90m[DEBUG][39m[0m: File "/home/bobf/ex/regression/.buildozer/android/platform/build-arm64-v8a/build/other_builds/atom/arm64-v8a__ndk_target_21/atom/setup.py", line 15, in
[1m[90m[DEBUG][39m[0m: raise RuntimeError(
[1m[90m[DEBUG][39m[0m: RuntimeError: Missing setup required dependencies: cppy. Installing through pip as recommended ensure one never hits this issue.
```

Start by examining the enaml recipe's setup.py and reproducing the Android build failure shown in the logs. Investigate why cppy does not provide CppyBuildExt in the host Python environment; done means the recipe builds without the reported ImportError.

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