Issue Description:

If a package uses XCTest in a normal target (not a test target), it fails to build in the generated Xcode project for iOS and tvOS. Here is an example such target:

import XCTest
open class SpecializedTestCase : XCTestCase {
    open override func setUp() {
        print("Doing specialized set‐up...")
    }
}

• Opening in Xcode by double‐clicking Package.swift and building for iOS will succeed, both the device and simulator.

• generate-xcodeproj and then building for iOS or tvOS succeeds for the simulator.

But:

• generate-xcodeproj and then building for iOS or tvOS fails for the device.

The exact error is:

ld: warning: Could not find or use auto-linked framework 'XCTest'
Undefined symbols for architecture arm64:
  "_OBJC_CLASS_$_XCTestCase", referenced from:
      type metadata for MyTarget.SpecializedTestCase in SpecializedTestCase.o
  "_OBJC_METACLASS_$_XCTestCase", referenced from:
      _OBJC_METACLASS_$__TtC18MyTarget8SpecializedTestCase in SpecializedTestCase.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Additional notes:

• #if canImport(XCTest) does not help.

• macOS works fine, but it has no device‐simulator distinction.

• watchOS does not work in this situation at all, but that is a separate bug.