Fix some warnings in building LLDB.

Differential Revision: https://reviews.llvm.org/D57413

llvm-svn: 352557
diff --git a/lldb/source/Plugins/Language/ObjC/NSArray.cpp b/lldb/source/Plugins/Language/ObjC/NSArray.cpp
index 96212cf..9eec28b 100644
--- a/lldb/source/Plugins/Language/ObjC/NSArray.cpp
+++ b/lldb/source/Plugins/Language/ObjC/NSArray.cpp
@@ -171,13 +171,8 @@
     PtrType _data;
     uint32_t _offset;
     uint32_t _size;
-    union {
-      PtrType _mutations;
-      struct {
-        uint32_t _muts;
-        uint32_t _used;
-      };
-    };
+    uint32_t _muts;
+    uint32_t _used;
   };
     
   using NSArrayMSyntheticFrontEnd =