[6.0] WiX: add `SwiftMacros.dll` to the image

[rintaro]

Cherry-pick https://github.com/apple/swift-installer-scripts/pull/295 into release/6.0

• Explanantion: This adds an additional DLL to the Windows toolchains. 'SwiftMacros.dll' includes macro implementations for stdlib. e.g. 'TaskLocal'
• Scope: Standard library macros in Windows toolchains
• Risk: Low. Just adding a DLL where it was supposed to be.
• Testing: Locally confirmed that stdlib macros TaskLocal work
• Issue: rdar://128092675
• Reviewer: @compnerd