Tentative fix for r351701 and gcc 6.2 build on ubuntu

llvm-svn: 351706
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 90c931f..0598da2 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -11731,19 +11731,19 @@
   };
 
   struct Usage {
-    Expr *Use = nullptr;
+    Expr *Use;
     SequenceTree::Seq Seq;
 
-    Usage() = default;
+    Usage() : Use(nullptr), Seq() {}
   };
 
   struct UsageInfo {
     Usage Uses[UK_Count];
 
     /// Have we issued a diagnostic for this variable already?
-    bool Diagnosed = false;
+    bool Diagnosed;
 
-    UsageInfo() = default;
+    UsageInfo() : Uses(), Diagnosed(false) {}
   };
   using UsageInfoMap = llvm::SmallDenseMap<Object, UsageInfo, 16>;