[Dependency Scanning] Disable validation of Swift dependency modules' existing pre-built candidate binary module files in the scanner, on a non-caching build.

[artemcm]

As-is, this default interferes with the incremental build machinery which conservatively assumes that binary module dependencies must cause dependents to be re-built.

[artemcm]

@swift-ci test

[artemcm]

https://github.com/swiftlang/swift-driver/pull/1673 @swift-ci test