X87: [stubs] Refactor StringCompareStub and use it for HStringCompareAndBranch.

src/x87/lithium-x87.h

Index: src/x87/lithium-x87.h
diff --git a/src/x87/lithium-x87.h b/src/x87/lithium-x87.h
index b2ceadb841de162dc5874dced580ddea8a675c7f..cc1a43fbaf56516af0494a3c9ade3a248e0fc1f3 100644
--- a/src/x87/lithium-x87.h
+++ b/src/x87/lithium-x87.h
@@ -1067,7 +1067,7 @@ class LStringCompareAndBranch final : public LControlInstruction<3, 0> {
     inputs_[2] = right;
   }
 
-  LOperand* context() { return inputs_[1]; }
+  LOperand* context() { return inputs_[0]; }
   LOperand* left() { return inputs_[1]; }
   LOperand* right() { return inputs_[2]; }