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

lib/Frontend/ModuleInterfaceSupport.cpp

@@ -163,7 +163,8 @@ static void
 diagnoseDeclShadowsModule(ModuleInterfaceOptions const &Opts,
                           TypeDecl *shadowingDecl, ModuleDecl *shadowedModule,
                           ModuleDecl *brokenModule) {
-  if (Opts.PreserveTypesAsWritten || shadowingDecl == shadowedModule)
+  if (Opts.PreserveTypesAsWritten || Opts.AliasModuleNames ||
+      shadowingDecl == shadowedModule)
     return;
 
   shadowingDecl->diagnose(