[turbofan] Fix liveness analysis for let variable in TDZ.

test/mjsunit/compiler/regress-variable-liveness-let.js

Index: test/mjsunit/compiler/regress-variable-liveness-let.js
diff --git a/test/mjsunit/regress/regress-crbug-505354.js b/test/mjsunit/compiler/regress-variable-liveness-let.js
similarity index 78%
copy from test/mjsunit/regress/regress-crbug-505354.js
copy to test/mjsunit/compiler/regress-variable-liveness-let.js
index 61c40c44dacb4091b482547cffbe6d4b3eeccb32..4c6b6936e58543844ec2684d56abd898217ce6cd 100644
--- a/test/mjsunit/regress/regress-crbug-505354.js
+++ b/test/mjsunit/compiler/regress-variable-liveness-let.js
@@ -4,11 +4,12 @@
 
 // Flags: --allow-natives-syntax --turbo-filter=f
 
+"use strict";
+
 function f() {
-  "use strict";
-  try {
-    for (let i = 0; i < 10; i++) {}
-  } catch(e) {}
+  %DeoptimizeNow();
+  let x = 23;
 }
+
 %OptimizeFunctionOnNextCall(f);
 f();