Enable -Wunused-private-field with -Wunused.

It found a lot of cruft in LLVM that I removed last week and I couldn't find any
false positives. Time to give it more testing.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158317 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/FixIt/fixit.cpp b/test/FixIt/fixit.cpp
index f5338cf..6a081e7 100644
--- a/test/FixIt/fixit.cpp
+++ b/test/FixIt/fixit.cpp
@@ -54,7 +54,7 @@
 }
 
 namespace rdar7796492 {
-  class A { int x, y; A(); };
+  struct A { int x, y; A(); };
 
   A::A()
     : x(1) y(2) { // expected-error{{missing ',' between base or member initializers}}