Fix undefined behavior that is caused by not always initializing a bool.

The fix in r310994 is incomplete, as moveFromAndCancel can set the
pointer without initializing OldIsSpeculativelyEvaluating.

llvm-svn: 311070

clang/lib/AST/ExprConstant.cpp

@@ -984,6 +984,7 @@ namespace {
     void moveFromAndCancel(SpeculativeEvaluationRAII &&Other) {
       Info = Other.Info;
       OldStatus = Other.OldStatus;
+      OldIsSpeculativelyEvaluating = Other.OldIsSpeculativelyEvaluating;
       Other.Info = nullptr;
     }