[modules] Add missing test file for b21ee08 (#129221)

The commit missed a test file.

Author: hokein

clang/test/Modules/pr28744.cpp

@@ -0,0 +1,17 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -std=c++11 -I%S/Inputs/PR28794 -verify %s
+// RUN: %clang_cc1 -std=c++11 -fmodules -fmodule-map-file=%S/Inputs/PR28794/module.modulemap -fmodules-cache-path=%t -I%S/Inputs/PR28794/ -verify %s
+
+#include "Subdir/Empty.h"
+#include "LibAHeader.h"
+
+BumpPtrAllocatorImpl<> &getPreprocessorAllocator();
+class B {
+  struct ModuleMacroInfo {
+    ModuleMacroInfo *getModuleInfo() {
+      return new (getPreprocessorAllocator()) ModuleMacroInfo();
+    }
+  };
+};
+
+// expected-no-diagnostics