Teach The AST Demangler About Module ABI Names

Use the current module's ABI name to resolve references in mangled names. This
is a targeted fix for a more general problem of opaque result types from
protocols that have moved modules with @_originallyDefinedIn.

Resolves rdar://119212609

Author: Robert Widmann

lib/AST/ASTDemangler.cpp

@@ -1031,7 +1031,10 @@ ASTBuilder::createTypeDecl(NodePointer node,
 ModuleDecl *
 ASTBuilder::findModule(NodePointer node) {
   assert(node->getKind() == Demangle::Node::Kind::Module);
-  const auto &moduleName = node->getText();
+  const auto moduleName = node->getText();
+  if (Ctx.MainModule && Ctx.MainModule->getABIName().is(moduleName))
+    return Ctx.MainModule;
+
   return Ctx.getModuleByName(moduleName);
 }