Ensure there is stack usage in stack size warning test

r359906 broke this because the only stack usage was from a spill which
can be avoided since the only block is a return.

llvm-svn: 359918
diff --git a/clang/test/Misc/backend-stack-frame-diagnostics-fallback.cpp b/clang/test/Misc/backend-stack-frame-diagnostics-fallback.cpp
index 8ae8c55..332dd22 100644
--- a/clang/test/Misc/backend-stack-frame-diagnostics-fallback.cpp
+++ b/clang/test/Misc/backend-stack-frame-diagnostics-fallback.cpp
@@ -14,5 +14,7 @@
 
   // CHECK: warning: stack frame size of {{[0-9]+}} bytes in function 'frameSizeThunkWarning::B::f'
   // CHECK: warning: stack size limit exceeded ({{[0-9]+}}) in {{[^ ]+}}
-  void B::f() { }
+  void B::f() {
+    volatile int x = 0; // Ensure there is stack usage.
+  }
 }