Add flag to verify just-emitted module interfaces

The driver can now schedule jobs which typecheck just-emitted module interfaces to ensure that they can be consumed later. This can be enabled manually by passing `-verify-emitted-module-interface` to the driver.

lib/Driver/ToolChain.cpp

@@ -111,6 +111,7 @@ std::unique_ptr<Job> ToolChain::constructJob(
       CASE(GeneratePCHJob)
       CASE(AutolinkExtractJob)
       CASE(REPLJob)
+      CASE(VerifyModuleInterfaceJob)
 #undef CASE
     case Action::Kind::Input:
       llvm_unreachable("not a JobAction");