XCBuild logs `unexpected mutating task` for WatchKit target

Number:rdar://34950052 Date Originated:11-Oct-2017 22:58
Status:Duplicate of 35488529 (closed) Resolved:Probably Xcode 9.3b4
Product:Developer Tools Product Version:Xcode 9.0 (9A235)
Classification:Other Bug Reproducible:I didn't try
When doing a clean build with XCBuild on our app including a WatchKit target, XCBuild emits this warning:

warning: unexpected mutating task ('CodeSign .../build/Products/Debug-watchsimulator/Watch.app') with no relation to prior mutator ('Ditto /Users/ksmiley/dev/.../build/Products/Debug-watchsimulator/Watch.app/Watch /Applications/Xcode.app/Contents/Developer/Platforms/WatchSimulator.platform/Developer/SDKs/WatchSimulator4.0.sdk/Library/Application\ Support/WatchKit/WK') (in target 'Watch')

Steps to Reproduce:
1. Switch to the new build system, and clean
2. Build

Expected Results:
There are no warnings

Actual Results:
This WatchKit warning is emitted

Xcode 9.0 (9A235)

See the attached log for more details


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