[C++ interop] A Swift executable target that depends on a Swift library target that enables C++ interop should tell Swift to link using clang++, even when C++ interop is not enabled in the executable target

[hyp]

Description

C++ interoperability can be enabled using the new .interoperabilityMode(.Cxx) setting.
We want to support a case where a Swift library target can enable C++ interoperability, but still be imported into another Swift target that doesn't enable C++ interoperability. That works today now that swiftlang/swift#65948 is fixed.
However, when an executable Swift target that depends on such Swift target gets linked, it doesn't use clang++ to link, i.e. it thinks that it can link the program as if C++ interop was not enabled in the entire dependency tree.

Expected behavior

SwiftPM should detect when an executableTarget depends on a Swift target that enables C++ interop and pass a flag to Swift driver that tells it that it should link as if interop is enabled.

Actual behavior

No response

Steps to reproduce

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Swift Package Manager version/commit hash

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Swift & OS version (output of swift --version ; uname -a)

No response