[cxx-interop] Do not install binary .swiftmodule files for the overlays

[egorzhdan]

This fixes a deserialization failure in the compiler that occurred while loading the CxxStdlib overlay module:

Cross-reference to module 'Swift'
... Optional
... some
... with type <τ_0_0 where τ_0_0 : ~Copyable, τ_0_0 : ~Escapable> (Optional<τ_0_0>.Type) -> (τ_0_0) -> Optional<τ_0_0>

This was happening because the overlays were built against a different version of the Swift stdlib than is being used. The compiler is able to rebuild the Cxx and CxxStdlib modules from their textual interfaces. Let's use that feature unconditionally in production toolchains to avoid this kind of binary incompatibilities.

rdar://150416863

[egorzhdan]

@swift-ci please smoke test

[j-hui]

LGTM

[compnerd]

CC: @etcwilde

[etcwilde]

Swift interfaces are only valid when library evolution is enabled. The platforms that do not have ABI stability do not have library evolution enabled, and so must use the binary swift module. We will need to continue installing the module on those platforms until they either have library evolution enabled or the textual interfaces are able to describe the layout of structs.

[xymus]

@etcwilde Is it the new build system that doesn't enable library-evolution on Windows? In the log above I see the swiftinterface being installed to /usr/lib/swift/windows/CxxStdlib.swiftmodule/aarch64-unknown-windows-msvc.swiftinterface and I was under the impression that our libraries had the same configuration on all platforms library-evolution wise even if on some of them we don't rely on ABI stability.

[compnerd]

AFAIK, library evolution is not enabled on Windows (unless someone changed the default underneath us). The old build system does emit the swift interface (and it is being shipped). The new build system implementation ties it explicitly to the library evolution mode, and I don't think that we should be enabling that on Windows currently.

[egorzhdan]

Thanks @etcwilde @compnerd, I changed this to only exclude binary swiftmodules on Darwin.

[egorzhdan]

@swift-ci please smoke test

[egorzhdan]

@swift-ci please build toolchain macOS

[egorzhdan]

@swift-ci please test Windows

[egorzhdan]

Oops, forgot to disable the auto-merger on this one... Happy to address any feedback post-merge.