Building swift_library targets with Bazel fails

An example message is:

(reformatted for readability)

```
:: error: Failed to find an output artifact for target ~/Library/Developer/Xcode/DerivedData/HammerLyft-apdrvgdqsckgxbeluodmnicxohsd/Build/Products/Debug-iphonesimulator/libArchitectureCore-Bazel.a
in output map {
u'generated_sources': [
[u'bazel-out/ios_x86_64-fastbuild/bin/Modules/ArchitectureCore/ArchitectureCore-Swift.h', u'Modules/ArchitectureCore/ArchitectureCore-Swift.h'],
[u'bazel-out/ios_x86_64-fastbuild/bin/Modules/ArchitectureCore/ArchitectureCore.swiftmodule', u'Modules/ArchitectureCore/ArchitectureCore.swiftmodule'],
[u'bazel-out/ios_x86_64-fastbuild/bin/Modules/ArchitectureCore/ArchitectureCore.modulemaps/module.modulemap', u'Modules/ArchitectureCore/ArchitectureCore.modulemaps/module.modulemap']
],
u'has_dsym': False
}
```

Start by reproducing the reported swift_library build with the example output and inspect how XCHammer handles the Bazel output map for the generated library artifact. The work is done when swift_library targets build successfully and the expected library output is found without the reported error.

Written by the indexing model from the issue text.