Fix infinite lookup importing forward declarations from bridging header

Author: NuriAmari

lib/ClangImporter/ClangImporter.cpp

@@ -1422,6 +1422,7 @@ ClangImporter::create(ASTContext &ctx,
     new (ctx) ClangModuleUnit(*importedHeaderModule, importer->Impl, nullptr);
   importedHeaderModule->addFile(*importer->Impl.ImportedHeaderUnit);
   importedHeaderModule->setHasResolvedImports();
+  importedHeaderModule->setIsNonSwiftModule(true);
 
   importer->Impl.IsReadingBridgingPCH = false;
 

test/ClangImporter/Inputs/incomplete_objc_types_bridging_header.h

@@ -0,0 +1,4 @@
+@class ForwardDeclaredInterface;
+
+ForwardDeclaredInterface *CFunctionReturningAForwardDeclaredInterface();
+void CFunctionTakingAForwardDeclaredInterface(ForwardDeclaredInterface *param);

test/ClangImporter/incomplete_objc_types_bridging_header.swift

@@ -0,0 +1,6 @@
+// RUN: %target-swift-frontend -import-objc-header %S/Inputs/incomplete_objc_types_bridging_header.h -enable-upcoming-feature ImportObjcForwardDeclarations -enable-objc-interop -typecheck %s
+
+// REQUIRES: objc_interop
+
+let foo = CFunctionReturningAForwardDeclaredInterface()
+CFunctionTakingAForwardDeclaredInterface(foo)