[turbofan] Fix assert caused by bogus merging of out-of-scope CodeAssembler variables

src/compiler/code-assembler.cc

Index: src/compiler/code-assembler.cc
diff --git a/src/compiler/code-assembler.cc b/src/compiler/code-assembler.cc
index b9d11af4874366c725dca1f900ff44a12095ec8c..9bc40258c8150fed693870f43e62a3ca89d79767 100644
--- a/src/compiler/code-assembler.cc
+++ b/src/compiler/code-assembler.cc
@@ -600,10 +600,12 @@ class CodeAssembler::Variable::Impl : public ZoneObject {
 
 CodeAssembler::Variable::Variable(CodeAssembler* assembler,
                                   MachineRepresentation rep)
-    : impl_(new (assembler->zone()) Impl(rep)) {
-  assembler->variables_.push_back(impl_);
+    : impl_(new (assembler->zone()) Impl(rep)), assembler_(assembler) {
+  assembler->variables_.insert(impl_);
 }
 
+CodeAssembler::Variable::~Variable() { assembler_->variables_.erase(impl_); }
+
 void CodeAssembler::Variable::Bind(Node* value) { impl_->value_ = value; }
 
 Node* CodeAssembler::Variable::value() const {