LICM shouldn't hoist nodes if hoisted nodes exited in that code block

LICM shouldn't hoist nodes if hoisted nodes exited in that code block
https://bugs.webkit.org/show_bug.cgi?id=185126

Reviewed by Saam Barati.

JSTests:

I found this bug by accident when I was writing this test for something else.

This change also speeds up other benchmarks of this case that we already had. They are all called
the licm-dragons tests.

* microbenchmarks/licm-dragons-two-structures.js: Added.
(foo):

Source/JavaScriptCore:

This change is just restoring functionality that we've already had for a while. It had been
accidentally broken due to an unrelated CodeBlock refactoring.

* dfg/DFGLICMPhase.cpp:
(JSC::DFG::LICMPhase::attemptHoist):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@231185 268f45cc-cd09-0410-ab3c-d52691b4dbfc