[SoM] Promote "module compiled with Swift X cannot be imported in Swift Y" to non-verbose

[chamons]

I spent too long today trying to figure why I was getting this:

Warnings and errors

Error (Fatal): Unable to find module contents for module SwiftIgPay. (CompilerException)```

Only upon adding --verbose did I get the useful part:

<unknown>:0: error: module compiled with Swift 4.2 cannot be imported in Swift 4.0.3: /var/folders/gc/7vct49652r1df_tp36ffvph00000gn/T/99dfae57-abce-4cb8-965f-880b61f48123/SwiftIgPay.swiftmodule

I believe this should be part of the error text on non-verbose, maybe a top level error itself?