swift234

[driver] Added support for adding a MergeModuleJobAction to the Action graph.

Updated Driver::OutputMode to also contain a ShouldGenerateModule field.
Updated Driver::getOutputMode() to set OutputMode::ShouldGenerateModule appropriately.
Updated Driver::buildActions() to insert a MergeModuleJobAction into the Action graph if the Driver’s OutputMode indicates that a module should be generated.

Swift SVN r12492