ModuleInterface: Don't warn on name conflict when the alias workaround is enabled
This warning is designed to be an early report of name conflicts in
swiftinterfaces caused by a type having the same name as a module.
Make sure we silence this warning when the workaround
-alias-module-names-in-module-interface is enabled. This is what we
already do for -module-interface-preserve-types-as-written.
rdar://132990400