swift234

[driver] Added support for determining a better output for a merge module Command.

First, prefer -module-output-path over any other options when binding the output
for a merge module Command. If that’s not set, use the same behavior as other
intermediate outputs, but use the module name as the base name (instead of the
BaseInput, which is not descriptive enough for a swiftmodule).

This does not yet handle the case where the emitted module should be treated as
a top-level output, even though it’s not the top-level job (essentially,
whenever -emit-module is passed but the driver isn't in EmitModuleOnly mode).

Swift SVN r12500