fix testcase to avoid -emit-ir

Author: hyp

test/Interop/SwiftToCxx/structs/zero-sized-struct-in-cxx.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend %s -typecheck -emit-ir -module-name Structs -clang-header-expose-public-decls -emit-clang-header-path %t/structs.h
+// RUN: %target-swift-frontend %s -typecheck -module-name Structs -clang-header-expose-public-decls -emit-clang-header-path %t/structs.h
 // RUN: %FileCheck %s < %t/structs.h
 
 // CHECK: namespace Structs {